* Add support for blacklisted_cdata_regex being plural.
* Remove obsolete INVALID_CDATA_CSS_IMPORTANT error code.
* Add new INVALID_CDATA_CSS_I_AMPHTML_NAME error code.

Fixes #4319

…phtml-2004041903580

* 'develop' of github.com:ampproject/amp-wp: (48 commits)
  Bump https-proxy-agent from 2.2.2 to 2.2.4 (#4596)
  Update dependency babel-jest to v25.3.0 (#4550)
  Update dependency core-js to v3.6.5 (#4558)
  For the 'Preview AMP' button, use a title instead of a tooltip (#4601)
  Bump stable tag to 1.5.3
  Fix handling of Mustache templates (#4583)
  Stub request based on test scenario (#4588)
  Return early instead of storing eventual return value in variable
  Improve phpdoc and logic conditions
  Update links in pull request template
  Update contributing.md with link to wiki
  Remove engineering.md now that it is on the wiki
  Remove project-management.md since only applicable to Stories
  Add conditions for comment feed, trackback, robots, and favicon
  Fix typo in global phpdoc
  Update tests after block-library/style.css changes in Gutenberg 7.9 (#4579)
  Remove special conditions for Reader mode; remove need for $exit condition in redirects
  Fix translators comment
  Add comment explaining short-circuit behavior when query var is present
  Update version for _doing_it_wrong() from 1.5.3 to 1.6.0
  ...