Add event.schedule context for schedule actions task (#37320) (#37348)

Backport #37320 by @lunny

Fix #35452

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

services/actions/schedule_tasks_test.go

@@ -0,0 +1,41 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package actions
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/modules/json"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWithScheduleInEventPayload(t *testing.T) {
+	t.Run("adds schedule to existing payload", func(t *testing.T) {
+		payload := `{"ref":"refs/heads/main"}`
+		updated := withScheduleInEventPayload(payload, "*/5 * * * *")
+
+		event := map[string]any{}
+		assert.NoError(t, json.Unmarshal([]byte(updated), &event))
+		assert.Equal(t, "*/5 * * * *", event["schedule"])
+		assert.Equal(t, "refs/heads/main", event["ref"])
+	})
+
+	t.Run("keeps empty payload", func(t *testing.T) {
+		updated := withScheduleInEventPayload("", "37 12 5 1 2")
+		assert.Empty(t, updated)
+	})
+
+	t.Run("keeps payload when schedule empty", func(t *testing.T) {
+		payload := `{"ref":"refs/heads/main"}`
+		updated := withScheduleInEventPayload(payload, "")
+		assert.Equal(t, payload, updated)
+	})
+
+	t.Run("keeps payload when malformed JSON", func(t *testing.T) {
+		payload := `not a json object`
+		updated := withScheduleInEventPayload(payload, "*/5 * * * *")
+		assert.Equal(t, payload, updated)
+	})
+}