fix(actions): allow larger scheduled workflows (#38985)

MySQL stores `action_schedule.content` as `BLOB`, limiting scheduled
workflow definitions to 65,535 bytes. Oversized workflows fail schedule
refresh and can also suppress default-branch push handling.

Store scheduled workflow content as `LONGBLOB`, migrate existing MySQL
columns, and cover the migration by persisting 65,536 bytes.

Fixes https://github.com/go-gitea/gitea/issues/38613

modelmigration/v28/v349.go

@@ -0,0 +1,29 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v28
+
+import (
+	"context"
+
+	"gitea.dev/modelmigration/base"
+	"gitea.dev/modules/setting"
+
+	"xorm.io/xorm/schemas"
+)
+
+func ExpandActionScheduleContent(ctx context.Context, x base.EngineMigration) error {
+	if !setting.Database.Type.IsMySQL() {
+		return nil
+	}
+
+	return base.ModifyColumn(ctx, x, "action_schedule", &schemas.Column{
+		Name: "content",
+		SQLType: schemas.SQLType{
+			Name: "LONGBLOB",
+		},
+		Length:         0,
+		Nullable:       true,
+		DefaultIsEmpty: true,
+	})
+}