Automatic merge from submit-queue (batch tested with PRs 56446, 56437). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Fix GC sync race condition
Remove faulty diff detection logic from GC sync which leads to a race
condition: If the GC's discovery client is returning a fully up to date
view of server resources during the very first GC sync, the sync
function will never sync monitors or reset the REST mapper unless
discovery changes again. This causes REST mapping to fail for any custom
types already present in discovery.
Fixes https://github.com/kubernetes/kubernetes/issues/56262.
```release-note
NONE
```
/cc @liggitt @caesarxuchao
7ce780d52e