Fix flaky Mononoke Git integration test

Summary: `test-mononoke-git-server-pull.t` when run in `dev` mode fails every now and then because the latest tag gets imported does not become available in the WBC of Mononoke Git server. This diff modifies the test to wait for the actual tag update instead of waiting for the master bookmark.

Reviewed By: gustavoavena, YousefSalama, singhsrb

Differential Revision: D67521061

fbshipit-source-id: c9b1ca322e41e5a16bab3fd6b7317441a7c91be2

eden/mononoke/tests/integration/mononoke_git_server/test-mononoke-git-server-pull.t

@@ -71,9 +71,7 @@
 # Pull the Git repo from Mononoke
   $ cd $REPONAME
 # Wait for the warm bookmark cache to catch up with the latest changes
-  $ wait_for_git_bookmark_move HEAD $current_head
-# Wait for the warm bookmark cache to catch up with the latest changes
-  $ wait_for_git_bookmark_move HEAD $current_head
+  $ wait_for_git_bookmark_create refs/tags/last_tag
   $ quiet git_client pull
 # Verify that we get the same Git repo back that we started with
   $ git rev-list --objects --all | git cat-file --batch-check='%(objectname) %(objecttype) %(rest)' | sort > $TESTTMP/new_object_list