roll_merge_gerrit.py now loops, waiting for the merge to be submitted.
Once it is, it adds a tag with the version number.

Bug: v8:12849
Change-Id: I7c2765877efad2ccbe082b984642f5e989dc3c8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3705379Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81150}