Built-in test maintenance: skipped tests, warnings

[MathieuLamiot]

Context Logs from WP Rocket CI are messy when it comes to testing. We have a lot of warnings about:

• Deprecations
• Skipped tests (flagged as such, or skipped by data provider)
• Database errors etc.

Expected behavior We should clean the CI logs and fix the reported issues:

• Fix deprecations
• If tests are skipped on purpose, consider making them pass or removing them completely?
• If tests are skipped but not on purpose, fix them.
• Fix other errors

This might not be a win in one go, but baby steps with incremental PRs are fine. As long as we reduce noise on the CI 👍

Related pull requests:

• [x] #6622
• [x] #6623
• [ ] #6627