Update wp-env and some ETK PHP fixes

[noahtallen]

As I began working @tyxla's comment here (#79097 (comment)), I realized it'd be good to update various wp-env/ETK things (which I've been putting off for a while).

Proposed Changes

It's been a while since I touched wp-env in Calypso. This updates our config to make it compatible with new wp-env versions, which in turn means we're updating phpunit and setting a newer PHP version. As a result, there were a few other things to fix too.

Importantly, there are some features in ETK which were not written to work in local environments. In fact, they crash when not running on Automattic infrastructure. I decided to leave fixes for these out of the PR to make it less risky, but the result is that some pages of wp-env do not work. I will follow up with teams to try to get this resolved.

Local Testing Instructions

1. Run docker
2. cd apps/editing-toolkit
3. Build the plugin (yarn build)
4. After running composer install, run yarn test:php locally.

Wpcom testing instructions

1. On your sandbox, run install-plugin.sh etk update-wp-env.
2. Sandbox a test site and load the "new page" editor
3. Verify the "page pattern picker" loads, and then use the three-dot info dropdown in the editor to check that the ETK version is the same as the one installed by install-plugin in step 1.
4. Verify that the help center and whats-new still load on wpcom.

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-74063

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-74063&env=jetpack

[noahtallen]

PHP 8 does not allow you to access arrays directly if the index doesn't exist.

[noahtallen]

PHP 8 noticed these fields were undefined when going through other tests, which probably means the mock data wasn't fully created in the first place.

[noahtallen]

this directory doesn't exist any more

[noahtallen]

The wp-env update basically meant that you should manage your own phpunit version instead of bundling it, so we do that here.

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for editing-toolkit

To test your changes on WordPress.com, run install-plugin.sh editing-toolkit update-wp-env on your sandbox.

To deploy your changes after merging, see the documentation: PCYsg-mMA-p2

[noahtallen]

I removed the risky aspects of this, so what remains is really basic test code (verified by CI), and wp-env configuration (verified by CI and myself). The other non-test PHP changes are basically just phpcbf autofixes.

After testing, I'm confident this is safe to merge 👍

[tyxla]

This is some great work @noahtallen 🙌 The wp-env version was quite behind the latest one.