chore: don't require branch to be synced with main to merge (#425)

Many recent changes (e.g. docs) don't need to be synced with `main` to be pretty confident they are safe to merge.

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://togithub.com/googleapis/python-bigquery-dataframes/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> 🦕

.github/sync-repo-settings.yaml

@@ -5,7 +5,7 @@ branchProtectionRules:
 # Defaults to `main`
 - pattern: main
   requiresCodeOwnerReviews: true
-  requiresStrictStatusChecks: true
+  requiresStrictStatusChecks: false
   requiredStatusCheckContexts:
     - 'conventionalcommits.org'
     - 'cla/google'