fix: address code review findings

internal/musicbrainz/sync.go

@@ -57,7 +57,7 @@ func SyncArtistDiscography(
 		if err != nil {
 			return nil, fmt.Errorf("sync artist discography: read artist filter options: %w", err)
 		}
-		filtered := cachedReleases[:0]
+		filtered := make([]database.ExternalRelease, 0, len(cachedReleases))
 		for _, r := range cachedReleases {
 			if opts.IgnoreSingles && r.Type == "Single" {
 				continue