On macOS check if git is a stub or not before importing gitpython.

[sheagcraig]

What does this PR do?

On a freshly installed macOS, accessing git triggers a GUI dialog prompting users to install the Developer Command Line Tools. This is a nuisance for users, and since Salt really only cares about whether git is present, if we can find another way... Well we did!

On macOS, first we do a which git. If the git we get back is the "standard" location, we then use the stock xcode-select -p command, to determine whether the Developer tools are installed. If they aren't, this git is actually a stub and will trigger the dialog.

What issues does this PR fix or reference?

Fixes: #58575

Previous Behavior

See issue; every Salt run, the gitfs module triggers the GUI dialog.

New Behavior

On macOS without the Developer Command Line Tools, no dialogs are shown.

Merge requirements satisfied?

• Docs
• Changelog - https://docs.saltstack.com/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

Yes

[weswhet]

actually I think we'll need to do a which git here and then only do a stub check if the git to be used is /usr/bin/git

[weswhet]

wow, thanks so much all! Thought for sure we weren't gonna get this in, in time. 💯 🥳 🎊 🍾