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

models/actions/schedule.go

@@ -30,8 +30,8 @@ type ActionSchedule struct {
 	Ref           string
 	CommitSHA     string
 	Event         webhook_module.HookEventType
-	EventPayload  string `xorm:"LONGTEXT"`
-	Content       []byte
+	EventPayload  string             `xorm:"LONGTEXT"`
+	Content       []byte             `xorm:"LONGBLOB"`
 	Created       timeutil.TimeStamp `xorm:"created"`
 	Updated       timeutil.TimeStamp `xorm:"updated"`
 }