Disable repository messaging

[BenHenning]

Explanation

Core maintainers are no longer on break.

Essential Checklist

• The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• Any changes to scripts/assets files have their rationale included in the PR explanation.
• The PR follows the style guide.
• The PR does not contain any unnecessary code changes from Android Studio (reference).
• The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

N/A -- this is an infrastructure-only change.

[BenHenning]

PTAL @seanlip.

[github-actions]

Thanks for submitting this pull request! Some main reviewers
have taken time off for the next few weeks, so it may take a
little while before we can look at this PR. We appreciate your
patience while some of our team members recharge. We'll be fully
returning on 10 January 2022.

[oppiabot]

Hi @BenHenning, this PR is ready to be merged. Please address any remaining comments prior to merging, and feel free to merge this PR once the CI checks pass and you're happy with it. Thanks!