Validate anchors on relative links with docs tests

[viceice]

Describe the proposed change(s).

Additionally to #28561 we should also validate anchor correctness.
Otherwise those fail on docs build step.
Those simple errors often cause later failures which are only seen on our docs repo.

[renovate-release]

🎉 This issue has been resolved in version 38.28.1 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)
• 38.28.1

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