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/migrations.go

@@ -422,6 +422,7 @@ func prepareMigrationTasks() []*migration {
 		newMigration(346, "Add license_path column to repo_license and backfill", v28.AddLicensePathToRepoLicense),
 		newMigration(347, "Add watch options", v28.AddWatchOptions),
 		newMigration(348, "Recreate email_hash table for SHA256 avatar hashes", v28.RecreateEmailHashTable),
+		newMigration(349, "Expand action_schedule content column", v28.ExpandActionScheduleContent),
 	}
 	return preparedMigrations
 }