[git] gitGenerators.commits doesn't handle extracting commit hash properly

Sanity checks

• My issue relates to a specific CLI completion spec (e.g. git checkout is missing options in git completion spec). If your issue is more general, please create your issue here: withfig/fig
• I have searched github.com/withfig/autocomplete/issues and there are no duplicates of my issue
• I would like to work on this.

What CLI tool does this relate to?

git

Which statement makes the most sense?

There is a bug with this completion spec

Issue Details

Commit has length of 7 is assumed but not always correct:

https://github.com/withfig/autocomplete/blob/aef52acff84c45edde61ae610cc2c964802b9a38/src/git.ts#L119-L137