chore: build with Go 1.26; use Go 1.25 features (#10570)

WaitGroup.Go and built-in gomaxprocs handling.

Signed-off-by: Jakob Borg <jakob@kastelo.net>

lib/syncthing/utils.go

@@ -198,10 +198,8 @@ func TryMigrateDatabase(ctx context.Context, deleteRetention time.Duration) erro
 		fis := make(chan protocol.FileInfo, 50)
 		var writeErr error
 		var wg sync.WaitGroup
-		wg.Add(1)
 		writerDone := make(chan struct{})
-		go func() {
-			defer wg.Done()
+		wg.Go(func() { //nolint:contextcheck
 			defer close(writerDone)
 			var batch []protocol.FileInfo
 			files, blocks := 0, 0
@@ -238,7 +236,7 @@ func TryMigrateDatabase(ctx context.Context, deleteRetention time.Duration) erro
 			slog.Info("Migrated folder", "folder", folder, "files", files, "blocks", blocks, "duration", d.Truncate(time.Second), "filesrate", float64(files)/d.Seconds())
 			totFiles += files
 			totBlocks += blocks
-		}()
+		})
 
 		// Iterate the existing files
 		fs, err := olddb.NewFileSet(folder, ll)