Updating a PR doesn't trigger rally check

[forevergenin]

This one is similar to #161 but of more generic nature.

Bug Description

Updating a PR with new commits or amended commits doesn't trigger new rally check and drops any current failed checks as well.

To Reproduce

Steps to reproduce the behavior:

1. Create a new PR with invalid/missing rally information
2. The rally check will run and fail
3. Updated the PR with additional new commits or amended commits
4. The current checks are cleared and rally check is not re-triggered.

Expected behavior

Expected behavior is for rally checks to re-trigger and fail again

[forevergenin]

Adding pull_request.synchronize to the list of web hooks to listen to trigger rally check might fix this issue.

https://github.community/t/what-is-a-pull-request-synchronize-event/14784/4
https://docs.github.com/en/developers/webhooks-and-events/webhook-events-and-payloads#pull_request

[zkoppert]

I was able to reproduce this behavior.

[zkoppert]

Working on testing if pull_request.synchronize addresses this issue. Work being done on the multi-commit branch.