pre-commit: periodic garbage collection

How funny, I do not remember setting this up. It is useful nonetheless: thiago.perrotta ~ ❯ crontab -l 30 12 1-7 * 5 [ "$(( ($(date +\%-d)-1)/7+1 ))" -eq 1 ] && /opt/homebrew/bin/pre-commit gc >> /Users/thiago.perrotta/.cronlogs/pre-commit-gc.log 2>&1 thiago.perrotta ~ ❯ cat /Users/thiago.perrotta/.cronlogs/pre-commit-gc.log 2 repo(s) removed. 0 repo(s) removed. 3 repo(s) removed. 20 repo(s) removed. 10 repo(s) removed. 18 repo(s) removed. 2 repo(s) removed. 0 repo(s) removed. 0 repo(s) ...