fix: Use absolute (relative to repo root) path to supplied filename

[mattcen]

If a file is referenced from the subdir of a repository, the script confirms it exists and tacks the filename onto the URL, but doesn't check if the filename provided is relative to the repo root.

I couldn't immediately work out the best way to update the tests to:

1. Create a temp dir inside the existing temp repo
2. Create a new temp file within that new dir
3. Change CWD to the new dir
4. Run git-browse on that new file with a relative path

[github-actions]

This PR was closed because it has been stalled for 365 days with no activity. Feel free to make a new PR if you wish to continue

[spacewander]

@mattcen
Is this PR ready for review?

[mattcen]

@spacewander happy for review, with the caveat I never worked out how to update tests as per PR description

[spacewander]

Looks like we need to update the tests.

[spacewander]

Would you update other test files too?

[mattcen]

I could not immediately work out how they worked or how to update them in the time I had available, which is why this wasn't completed when I first opened the PR. I will try to take another look at them, but am not sure how soon that will be; any guidance or suggestions you can provide would be much appreciated.

[spacewander]

Maybe you can change

git-extras/tests/helper.py

Line 47 in 99207ee

return file[1:]

to return a full path name like os.path.relpath(file, self._cwd)?