Reduce time spent updating git clones

[szabgab]

We have cloned the git repositories of the 13,000 CPAN distributions that had a link to their git repo (out of the total of 40,000 distributions).
We would like to keep the up to-date, but git pull takes about 0.250 sec even if there is nothing to update. This means about 1 hour of processing time for the 13K distributions. Most of them without any changes.

We don't want to use the new release as the trigger to update the clone because a developer might make several changes to a repo without releasing a new version to CPAN. (e.g. setting up GitHub Actions).