Fix UnityPrint filename escaping in test runner

[swaldhoer]

Currently created code:

    if (parse_status < 0)
    {
      UnityPrint("foo/bar/more/bla"); // file extension missing
      UNITY_PRINT_EOL();
      return 0;
    }
    return parse_status;
  }

This is then fixed to become:

    if (parse_status < 0)
    {
      UnityPrint("foo/bar/more/bla.c"); // file extension added
      UNITY_PRINT_EOL();
      return 0;
    }
    return parse_status;
  }

(I needed to do apply this in the GitHub UI, please verify that I did not make copy-paste error in the web UI)