Refactor database connection (#37496)

Clean up legacy copied&pasted code, introduce the unique "database
connection" function. Move migration testing helper function
PrepareTestEnv to a separate package.

By the way, remove "shadow connection secrets" tricks: showing
connection string on UI is useless

---------

Co-authored-by: Nicolas <bircni@icloud.com>

models/migrations/v1_23/main_test.go

@@ -6,9 +6,9 @@ package v1_23
 import (
 	"testing"
 
-	"code.gitea.io/gitea/models/migrations/base"
+	"code.gitea.io/gitea/models/migrations/migrationtest"
 )
 
 func TestMain(m *testing.M) {
-	base.MainTest(m)
+	migrationtest.MainTest(m)
 }

models/migrations/v1_23/v302_test.go

@@ -6,7 +6,7 @@ package v1_23
 import (
 	"testing"
 
-	"code.gitea.io/gitea/models/migrations/base"
+	"code.gitea.io/gitea/models/migrations/migrationtest"
 	"code.gitea.io/gitea/modules/timeutil"
 
 	"github.com/stretchr/testify/assert"
@@ -44,7 +44,7 @@ func Test_AddIndexToActionTaskStoppedLogExpired(t *testing.T) {
 	}
 
 	// Prepare and load the testing database
-	x, deferable := base.PrepareTestEnv(t, 0, new(ActionTask))
+	x, deferable := migrationtest.PrepareTestEnv(t, 0, new(ActionTask))
 	defer deferable()
 
 	assert.NoError(t, AddIndexToActionTaskStoppedLogExpired(x))

models/migrations/v1_23/v304_test.go

@@ -6,7 +6,7 @@ package v1_23
 import (
 	"testing"
 
-	"code.gitea.io/gitea/models/migrations/base"
+	"code.gitea.io/gitea/models/migrations/migrationtest"
 	"code.gitea.io/gitea/modules/timeutil"
 
 	"github.com/stretchr/testify/assert"
@@ -33,7 +33,7 @@ func Test_AddIndexForReleaseSha1(t *testing.T) {
 	}
 
 	// Prepare and load the testing database
-	x, deferable := base.PrepareTestEnv(t, 0, new(Release))
+	x, deferable := migrationtest.PrepareTestEnv(t, 0, new(Release))
 	defer deferable()
 
 	assert.NoError(t, AddIndexForReleaseSha1(x))