Merge pull request #30401 from caesarxuchao/kubemark-gc-upstream

Automatic merge from submit-queue

Let load and density e2e tests use GC if it's on

I've run the 100 and 500 nodes tests and they both pass.

The test-infra half of the PR is https://github.com/kubernetes/test-infra/pull/369

cc @lavalamp

hack/verify-flags/known-flags.txt

@@ -505,3 +505,4 @@ whitelist-override-label
 windows-line-endings
 www-prefix
 zone-name
+garbage-collector-enabled