borgbackup: reenable fixed test (#404515)

Reported upstream in 2023 and couldn't reproduce it anymore on 1.4.1.

Author: mweinelt

pkgs/by-name/bo/borgbackup/package.nix

@@ -121,8 +121,6 @@ python.pkgs.buildPythonApplication rec {
     "test_get_keys_dir"
     "test_get_security_dir"
     "test_get_config_dir"
-    # https://github.com/borgbackup/borg/issues/6573
-    "test_basic_functionality"
   ];
 
   preCheck = ''