Prevent dangling GetAttribute calls (#18754)

It appears possible that there could be a hang due to unread data from the
repo-attribute command pipes. This PR simply closes these during the defer.

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/git/repo_language_stats_nogogit.go

@@ -88,7 +88,10 @@ func (repo *Repository) GetLanguageStats(commitID string) (map[string]int64, err
 					}
 				}()
 			}
-			defer cancel()
+			defer func() {
+				_ = checker.Close()
+				cancel()
+			}()
 		}
 	}