Add git dashes separator to some "log" and "diff" commands (#23606)

Add git dashes separator to some "log" and "diff" commands (#23606)

Reference:
https://github.com/go-gitea/gitea/issues/22578#issuecomment-1444180053

Credits to @tdesveaux , thank you very much for catching the problem. If
you'd like to open a PR, feel free to replace this one.

Git reports fatal errors for ambiguous arguments:

```
fatal: ambiguous argument 'refs/a...refs/b': unknown revision or path not in the working tree.
        Use '--' to separate paths from revisions, like this:
        'git <command> [<revision>...] -- [<file>...]'
```

So the `--` separator is necessary in some cases.