[Feature request]: Skip git fetch when cached repository already has the correct commit hash

[darkdragon-001]

Checklist

• [X] I agree to follow the Code of Conduct that this project adheres to.
• [X] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Suggestion

Some git modules (e.g. boost) have tons of git submodules. Checking them on every build takes several minutes(!) even though they are already checked out and uniquely pinned by the commit hash. This makes solving problems quite time-consuming...