Fix unreliable link test

[talldan]

Attempts to fix #13044. This failure only happens in CI (unable to reproduce locally) hence this PR

Description

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Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[talldan]

Hey @gziolo - I haven't really done any more to fix this one beyond a few changes to the test code. I wasn't able to work out why it was failing.

However, over the last 1-2 weeks I've been running the tests on travis in this branch on a daily basis, and I haven't seen a single failure of the test in question. I wonder if other code changes have resulted in this test becoming more stable 🤔

I think it might be worth trying to reintroduce the test— we can always disable it again if we see some failures.

[gziolo]

Let's reintroduce this test then :)

[youknowriad]

This is still failing in several PRs for me. Let's disable all the unstable tests we find.

[aduth]

This comment should have been removed.

[aduth]

This is still failing in several PRs for me. Let's disable all the unstable tests we find.

See #15059