required-review: Don't fail on case mismatch for @singleuser pseudo-teams

[anomiex]

Proposed changes:

GitHub usernames are case-insensitive but case-preserving. To match that logic, we want @singleuser to match SingleUser or whatever the actual username is.

This is complicated by the fact that "case-insensitive" can vary depending on what exactly GitHub is doing on their end, what version of Unicode they're using, and so on. So let's just ask GitHub's API for the correct casing of the username and use that instead of trying to work out all those edge cases ourself.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

#29318 (comment)

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Try changing the case of an @singleuser entry in .github/files/required-review.yaml and using the test.sh script to see how it handles an appropriate PR.

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

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This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

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The e2e test report can be found here. Please note that it can take a few minutes after the e2e tests checks are complete for the report to be available.

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[jeherve]

This looks good to me. 🚢