GH Actions: various updates to the workflows

[jrfnl]

GH Actions: don't run CS checks on main

... as the can't be fixed on main anyway. This would need a PR to develop.

(consistency with other workflows for the Yoast repos)

GH Actions/basics: tweak the workflow

• Split step which was running multiple commands into two steps and combine a couple of those commands into a single command for improved error management.
• Ensure all steps have a name.
• Remove redundant comment.

GH Actions/test: remove the experimental key from the matrix

... as, at this time, it isn't really needed.

GH Actions/test: remove unused steps for PHPCS 4.x

Testing against PHPCS 4.x-dev has not been possible for a while and development of that version looks to be stagnated anyway, so testing against it is not really relevant at this time.

This commit removes all references to testing against PHPCS 4.x from the workflow.

If/when testing against the next PHPCS major becomes relevant again, this can brought back and adjusted based on the reality at that time.

GH Actions: tweak the way the PHPCS/WPCS versions are set

Next iteration after PR #300.

YoastCS 3.0 will not just have PHPCS and WPCS as dependencies for the sniff tests, but also PHPCSUtils.

PR #300 already changed the logic of the workflow to take advantage of the Composer --prefer-lowest setting. This commit takes this yet another step further.

Stable vs Dev

As things were, the sniff tests were being run against the lowest supported CS dependencies and the development version of supported CS dependencies (with the exception of WPCS dev as WPCS 3.0.0 is not yet supported).

While testing against the dev versions of CS dependencies is relevant, it is more important that the tests safeguard that the sniffs work correctly on user-installable combinations of the CS dependencies.

Now, it could be argued that every single combination of the different versions of each of these dependencies should be tested, but that would make the matrix huge to little added benefit, especially as most of the time, the lowest and stable supported versions of CS dependencies will be the same for YoastCS (though not always, which still makes the distinction and running of tests against both lowest and stable relevant as it will allow for new releases of the CS dependencies automatically).

To that end, I'm changing the test matrices to test by default against the lowest and stable supported versions of dependencies with some select extra builds testing against the dev versions of supported CS dependencies.

PHP parse error linting will be run against all builds with the stable key now.

Note: stable is also the name used for the Composer sister-argument to --prefer-lowest: --prefer-stable, so should be clear-cut for anyone reading the workflow.

Consequences

Quicktest workflow:

• This will no longer contain exact versions of the CS dependencies in the test matrix, which should simplify workflow maintenance.
• The "Composer update" step for the dev dependencies has been adjusted. Instead of multiple commands, it now does all the updates in one combined command, which should make debugging of the workflow easier.
• One extra build has been added to test against dev dependencies.

Test workflow:

• The standard builds will now run against lowest and stable versions of dependencies and a number of extra builds have been added to test against dev versions of dependencies.
  I considered marking those as "allowed to fail" (continue-on-error), but decided against that as the sniffs should always be ready for the next minor/patch release of the CS dependencies.
• The commented out build against WPCS dev can now be removed as that will be handled via the "all CS dependencies" dev builds (once WPCS 3.0 is supported and re-enabled for update for the dev builds).
• The "Composer update" step for the dev dependencies has been adjusted. Instead of multiple commands, it now does all the updates in one combined command, which should make debugging of the workflow easier.
• The "Composer update" step for the lowest depencies has been adjusted to be more readable.
• Note that the direct Composer commands do not include --update-with-dependencies as our and our child dependencies overlap anyway.
• The code coverage builds will now run against lowest, and dev, which is basically the same as it was before.

Also note that the direct Composer command for updating the CS dependencies currently contain the --ignore-platform-req=php+ argument.
This is needed for PHP 8.x due to the max supported PHPUnit version being PHPUnit 7.x.
This CLI argument can be removed once upstream PR squizlabs/PHP_CodeSniffer#3803 has been merged.

[coveralls]

coverage: 97.815%. remained the same
when pulling 6131d41 on JRF/ghactions-update-workflows
into c3b064f on develop.

[jrfnl]

Note: this PR needs a one-time only change in the branch protection settings to account for the new build names.