Introduce testing workflow for the local Docker environment

[desrosj]

Currently, the PHPUnit test workflows rely on the local Docker environment, so it's tested as a part of that process. However, it's likely that this could change in the future, and there are conditions that are not currently covered by that workflow (running on Windows), and some commands for the environment that are not tested (env:logs, env:restart, etc.).

A new workflow should be created for confirming the local Docker environment continues working when related changes are made.

Trac ticket: https://core.trac.wordpress.org/ticket/62197

@Clorith I gave up on getting Windows to work. It seems that MacOS and Windows runners cannot run Docker, or at least there's no good guides for how to accomplish that.

That makes this workflow a bit less useful. Ideally we can confirm everything works on the platforms that our contributors are using. But there's probably still _some_ benefit to confirming that it works overall.

Merged in https://core.trac.wordpress.org/changeset/59491 and https://core.trac.wordpress.org/changeset/59492.