Have Danger check the format of GitHub issue links (#14684)

This PR updates the Danger rules to check for GitHub issue links that
aren't in the desired format:

<img width="916" alt="Screenshot 2024-07-17 at 5 11 48 PM"
src="https://github.com/user-attachments/assets/c77d3c28-3b09-44aa-a97f-03c2400df2e6">

We don't yet check that the links are exactly formatted as expected,
just that they aren't incorrectly formatted in the way that people
typically get it wrong.

Release Notes:

- N/A