Refactor integration test DecodeJSON calls to use generic return value (#37432)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wxiaoguang <2114189+wxiaoguang@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

tests/integration/actions_runner_test.go

@@ -86,10 +86,9 @@ func (r *mockRunner) registerAsRepoRunner(t *testing.T, ownerName, repoName, run
 	token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteRepository)
 	req := NewRequest(t, http.MethodPost, fmt.Sprintf("/api/v1/repos/%s/%s/actions/runners/registration-token", ownerName, repoName)).AddTokenAuth(token)
 	resp := MakeRequest(t, req, http.StatusOK)
-	var registrationToken struct {
+	registrationToken := DecodeJSON(t, resp, &struct {
 		Token string `json:"token"`
-	}
-	DecodeJSON(t, resp, &registrationToken)
+	}{})
 	r.doRegister(t, runnerName, registrationToken.Token, labels, ephemeral)
 }