Apparently, these gc() invocations rely on that the previous "git gc" packed
all refs so there are no loose refs to compare mtimes. If there were new (or
remaining) loose refs, mtime comparison could fail. I also added +1sec to
effectively turn off the keep_newer option, which isn't important in these
tests.
With my jj repo, the number of jj/keep refs went down from 87887 to 27733.
The .git directory size is halved, but we'll need to clean up extra and index
files to save disk space. "git gc --prune=now && jj debug reindex" passed, so
the repo wouldn't be corrupted.
#12
