check: Partially fix garbled output

When reporting an error for a tree, the output message can overlap with
the progress bar output, e.g. `error for tree e91ef6fb:napshots`.

The fix only applies for this specific message and does not work on
Windows.

cmd/restic/cmd_check.go

@@ -295,7 +295,11 @@ func runCheck(ctx context.Context, opts CheckOptions, gopts GlobalOptions, args
 	for err := range errChan {
 		errorsFound = true
 		if e, ok := err.(*checker.TreeError); ok {
-			Warnf("error for tree %v:\n", e.ID.Str())
+			var clean string
+			if stdoutCanUpdateStatus() {
+				clean = clearLine(0)
+			}
+			Warnf(clean+"error for tree %v:\n", e.ID.Str())
 			for _, treeErr := range e.Errors {
 				Warnf("  %v\n", treeErr)
 			}