Merge branch 'jk/fetch-check-graph-objects-fix' into maint-2.51

Under a race against another process that is repacking the
repository, especially a partially cloned one, "git fetch" may
mistakenly think some objects we do have are missing, which has
been corrected.

* jk/fetch-check-graph-objects-fix:
  fetch-pack: re-scan when double-checking graph objects