Add comment marking the end of database migrations in `1.19.0` (#22975)

There will be no more migrations in `1.19.0`

---------

Signed-off-by: Yarden Shoham <hrsi88@gmail.com>

models/migrations/migrations.go

@@ -461,6 +461,8 @@ var migrations = []Migration{
 	NewMigration("Alter gpg_key_import content TEXT field to MEDIUMTEXT", v1_19.AlterPublicGPGKeyImportContentFieldToMediumText),
 	// v243 -> v244
 	NewMigration("Add exclusive label", v1_19.AddExclusiveLabel),
+
+	// Gitea 1.19.0 ends at v244
 }
 
 // GetCurrentDBVersion returns the current db version