Fix actions concurrency groups cross-branch leak (#37311)

## Problem

Workflow-level concurrency groups were evaluated — and jobs were parsed
— before the run was persisted, so `run.ID` was `0` and `github.run_id`
in the expression context resolved to an empty string. Expressions like:

```yaml
concurrency:
  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
  cancel-in-progress: true
```

collapsed to `<workflow>-` on every push event (`head_ref` is empty on
push), so `cancel-in-progress` cancelled in-progress runs across
**unrelated branches**, not just the current one.

Reproduced on a 1.26 instance:
- push to `master` → `ci` run starts
- push to `feature-branch` → the `master` run gets cancelled

GitHub Actions' documented semantic: on push events `github.run_id` is
unique per run, so the group is unique → no cancellation; on PR events
`github.head_ref` is the source branch → cancellation is per-PR.

## Fix

Insert the run **before** parsing jobs or evaluating workflow-level
concurrency, so `run.ID` is populated in time for every expression that
reads `github.run_id` — not just the concurrency group, but also
`run-name`, job names, and `runs-on`.

`jobparser.Parse` now runs inside the `InsertRun` transaction, after
`db.Insert(ctx, run)`. Workflow-level concurrency evaluation runs next
and only mutates `run` in memory. All concurrency-derived fields
(`raw_concurrency`, `concurrency_group`, `concurrency_cancel`) plus
`status` and `title` are persisted in a single final `UpdateRun` at
end-of-transaction — one `INSERT` + one `UPDATE` per run in both the
concurrency and non-concurrency paths (matches pre-branch parity, one
fewer `UpdateRepoRunsNumbers` `COUNT` than the interim state).

`GenerateGiteaContext` now sets `run_id` from `run.ID` unconditionally;
every caller passes a persisted run.

**Verification**: tested end-to-end on a 1.26 deployment. Before the
patch, two successive `ci` pushes (one to master, one to a feature
branch) cross-cancelled each other. After the patch, the same pushes —
in both orders (master→branch, branch→master) — run to completion
simultaneously across 15+ runs with zero cancellations.

**Regression tests** in `services/actions/context_test.go`:
- `TestEvaluateRunConcurrency_RunIDFallback` — unit check that
`EvaluateRunConcurrencyFillModel` resolves `github.run_id` from
`run.ID`.
- `TestPrepareRunAndInsert_ExpressionsSeeRunID` — full-flow check: calls
`PrepareRunAndInsert` with `${{ github.run_id }}` in both `run-name` and
the concurrency group, then asserts the persisted `Title`,
`ConcurrencyGroup`, and `RawConcurrency` contain / survive the run's ID.
Re-ordering `db.Insert` relative to either parse or concurrency eval
fails this test.

## Relation to #37119

[#37119](https://github.com/go-gitea/gitea/pull/37119) also moves
concurrency evaluation into `InsertRun` but keeps it **before**
`db.Insert`, then tries to populate `run_id` only when `run.ID > 0` —
which is still `0` at that call site, so the cross-branch leak would
survive that PR as written. This PR fixes the ordering so that `run.ID`
is actually populated at eval time, and broadens it to cover parse-time
expression interpolation too.

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

services/actions/context_test.go

@@ -4,14 +4,86 @@
 package actions
 
 import (
+	"strconv"
 	"testing"
 
 	actions_model "code.gitea.io/gitea/models/actions"
 	"code.gitea.io/gitea/models/unittest"
 
+	act_model "github.com/nektos/act/pkg/model"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
+func TestEvaluateRunConcurrency_RunIDFallback(t *testing.T) {
+	// Unit-level check that EvaluateRunConcurrencyFillModel resolves
+	// github.run_id from run.ID. The full-flow regression — that run.ID is
+	// non-zero by the time evaluation happens — is in
+	// TestPrepareRunAndInsert_ExpressionsSeeRunID.
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	ctx := t.Context()
+
+	runA := unittest.AssertExistsAndLoadBean(t, &actions_model.ActionRun{ID: 791})
+	runB := unittest.AssertExistsAndLoadBean(t, &actions_model.ActionRun{ID: 792})
+
+	expr := &act_model.RawConcurrency{
+		Group:            "${{ github.workflow }}-${{ github.head_ref || github.run_id }}",
+		CancelInProgress: "true",
+	}
+
+	assert.NoError(t, EvaluateRunConcurrencyFillModel(ctx, runA, expr, nil, nil))
+	assert.NoError(t, EvaluateRunConcurrencyFillModel(ctx, runB, expr, nil, nil))
+
+	assert.Contains(t, runA.ConcurrencyGroup, "791")
+	assert.Contains(t, runB.ConcurrencyGroup, "792")
+	assert.NotEqual(t, runA.ConcurrencyGroup, runB.ConcurrencyGroup)
+}
+
+func TestPrepareRunAndInsert_ExpressionsSeeRunID(t *testing.T) {
+	// Regression for the cross-branch concurrency leak: github.run_id must
+	// be available during BOTH jobparser.Parse (run-name) and workflow-level
+	// concurrency evaluation. Re-ordering db.Insert relative to either step
+	// would leave run.ID at 0 and break this test.
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	ctx := t.Context()
+
+	content := []byte(`name: cross-branch
+run-name: "Run ${{ github.run_id }}"
+on: push
+concurrency:
+  group: group-${{ github.run_id }}
+  cancel-in-progress: true
+jobs:
+  hello:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`)
+
+	run := &actions_model.ActionRun{
+		Title:         "before parse",
+		RepoID:        4,
+		OwnerID:       1,
+		WorkflowID:    "expr-runid.yaml",
+		TriggerUserID: 1,
+		Ref:           "refs/heads/master",
+		CommitSHA:     "c2d72f548424103f01ee1dc02889c1e2bff816b0",
+		Event:         "push",
+		TriggerEvent:  "push",
+		EventPayload:  "{}",
+	}
+	require.NoError(t, PrepareRunAndInsert(ctx, content, run, nil))
+	require.Positive(t, run.ID)
+
+	persisted := unittest.AssertExistsAndLoadBean(t, &actions_model.ActionRun{ID: run.ID})
+	runIDStr := strconv.FormatInt(run.ID, 10)
+	assert.Equal(t, "Run "+runIDStr, persisted.Title)
+	assert.Equal(t, "group-"+runIDStr, persisted.ConcurrencyGroup)
+	// Rerun reads raw_concurrency from the DB to re-evaluate the group;
+	// see services/actions/rerun.go. Must survive the insert.
+	assert.NotEmpty(t, persisted.RawConcurrency)
+}
+
 func TestFindTaskNeeds(t *testing.T) {
 	assert.NoError(t, unittest.PrepareTestDatabase())