fix: drain migration channel on early return to prevent goroutine leak

runMigrations returned on the first error without draining the ret
channel. The reader goroutine (read/readUp/readDown) blocked forever
on a send once the PrefetchMigrations buffer filled, leaking the
goroutine plus any open migration file handles or HTTP bodies.

Added a deferred drain loop so the channel is fully consumed on all
return paths.

Author: simpleqt

migrate.go

@@ -721,6 +721,12 @@ func (m *Migrate) readDown(from int, limit int, ret chan<- interface{}) {
 // to stop execution because it might have received a stop signal on the
 // GracefulStop channel.
 func (m *Migrate) runMigrations(ret <-chan interface{}) error {
+	// Drain remaining items on early return so the reader goroutine can
+	// exit and release its resources (migration file handles, HTTP bodies).
+	defer func() {
+		for range ret {
+		}
+	}()
 	for r := range ret {
 
 		if m.stop() {