Release 3.9.0

[kasparsd]

Release Changelog

• Fix: Track changes to posts when using the block editor by making the Posts connector to run on both frontend and backend requests since block editor changes happen over the REST API #1264, props @coreymckrill.
• Fix: Don't store empty log event parameters #1307, props @lkraav.
• Development: Adjust the local development environment to use MariaDB containers for ARM processor compatabilty.

Release Checklist

• This pull request is to the master branch.
• Release version follows semantic versioning. Does it include breaking changes?
• Update changelog in readme.txt.
• Bump version in stream.php.
• Bump Stable tag in readme.txt.
• Bump version in classes/class-plugin.php.
• Draft a release on GitHub.

Change [ ] to [x] to mark the items as done.