Tiny headline adjustment for the Issue event types page

[abjerner]

Why:

The Issue event types page has a number of Event object properties headlines. All but one are H4s, as a single is a H3 instead.

As a H3 gets a link in the page navigation to the right, I thought I would change that to a H4 as well 😉

Since this is such a tiny change, I haven't created an issue.

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging.
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[welcome]

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[janiceilene]

@abjerner Thanks for opening a PR 👍 Please fill out the pull request template in the top comment in this pull request, then we'll get this up for review!

[abjerner]

@janiceilene I've updated the PR now. I wasn't sure about check list, but makes more sense now that the tests have completed.

[janiceilene]

Thanks so much @abjerner! I'll get this triaged for review ⚡

[lucascosti]

Thanks for fixing this, @abjerner!

[github-actions]

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