Mentions in Changelog send notifications

[jrjohnson]

Seems to be a recurrence of #427 except for Changelog summary. As an example this PR rdohms/chainlink#36 mentions me in the Changelog section and I got notified about it

[feelepxyz]

@jrjohnson yes will take a look at fixing this!

[pedropombeiro]

Curiously, only the first part of the string up to the first code fence (```registerLoader```) seems to have been sanitized (see the body element in https://api.github.com/repos/rdohms/chainlink/issues/36). This seems to point to a bug in the logic in sanitize_links_and_mentions, where instead of iterating through all the code fences, it considers everything after the start of the first code fence to be part of the code fence, and therefore ingests it as-is.

I've added a couple of tests in my fork that demonstrate the bug. If I have some spare time I'll take a look into fixing the implementation.

[feelepxyz]

@pombeirp yup nice find, I've got a fix here: #1426

[pedropombeiro]

Thanks @feelepxyz! I'll create a separate PR to handle an additional scenario with complex nested code fences too, to avoid false positives.

[jrjohnson]

Thank you!