remove .git extension

[bbrewington]

Summary

Very minor edit and admittedly pedantic, but the .git extension is really only needed for a "bare git repo" - explained pretty well here: https://stackoverflow.com/a/1734421

When cloning a repo at the top-level from GitHub, it's redundant and potentially misleading to include the .git extension

Changes

This is just a docs change, so don't anticipate any impact on automation

Task list

• [x] For workflow changes, I have verified the Actions workflows function as expected.
• [x] For content changes, I have reviewed the style guide.