Disable cron for SlackHQ Upstream Sync action

[timvaillancourt]

Description

This PR stops the SlackHQ Upstream Sync action from running on a cron schedule so it doesn't fight a POC being tested at https://github.com/slackhq/vitess-repo-syncer

[vmogilev]

A few Qs just so I understand how this works:

1. is the other repo now responsible for the sync of this repo?
2. if ^^^ is true, do we still need .github/workflows/slackhq_upstream_sync.yml, or this is just a quick test?

[timvaillancourt]

@vmogilev I'm testing two approaches at the moment:

1. The GitHub Action on slackhq/vitess itself. The drawback here is we must add a commit to the main branch for every merge/syncing and any changes to our slackhq_upstream_sync.yml. Example:
   

2. Running the GitHub Action from slack/vitess-repo-syncer with git push --force. This approach causes no new commits to main and sounds like the better approach, although it requires an extra private repo. Another benefit is we can edit the README.md to explain how it works, troubleshooting, etc

I'd like to keep both approaches while we decide which is best. For now disabling the cron schedule will prevent them from fighting each other

cc @tanjinx

[tanjinx]

here is we must add a commit to the main branch for every merge/syncing and any changes
@timvaillancourt I am no longer seeing those commits, do we confirm if this is true?

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[timvaillancourt]

Closing as the repo sync moved to a new repo