gracefully handle if git is not installed

[blmaier]

The following error occurs in _get_contributors() if git is not installed.

FileNotFoundError: [Errno 2] No such file or directory: 'git': 'git'

Treat this the same as if git fails, catch the error and print a warning.

[dhellmann]

Nice fix, thank you!

[blmaier]

Hi @dhellmann, is this blocked on the failing tests? They appear to be an unrelated issue with xmlrpc.

[dhellmann]

Yes, we will have to remove the use of the plugin that relies on that old XMLRPC interface so the tests work. I'm pretty sure that just means changing this line to set the flag to False

[dhellmann]

The "History Update" job is failing because there is no corresponding change in history.rst explaining this fix.

[blmaier]

I added a history entry.

For the XML issue, it appears to be an issue in this package here: https://github.com/sphinx-contrib/spelling/blob/main/sphinxcontrib/spelling/filters.py#L165-L166
The pypi documentation recommends switching to their JSON API. https://warehouse.pypa.io/api-reference/xml-rpc.html#list-packages

[blmaier]

I missed that the XML bug is an open issue here as well #227