This package combines the previously used PHPUnit_Polyfills with support for WordPress integration tests.

Needed to make tests compatible with multiple versions of PHPUnit.

This was deprecated in PHPUnit 8 and removed in PHPUnit 9, but the dms/phpunit-arraysubset-asserts means it can continue to be used for now.

PHPUnit 9 deprecates `assertObjectHasAttribute()`. `assertObjectHasProperty()` is not available until PHPUnit 10.1, and only available with PHPUnit-Polyfills 2.0.0, which doesn't seem compatible with unit tests running under WP 5.7/5.8.

This was deprecated in PHPUnit 8 in favour of more specific method names.

Use `assertStringNotContainsString()` instead.

- Removes constant that was making all tests run with multisite.
- Converts deprecations to exceptions to be true.

By marking certain tests as being in a `@group`, and excluding them, then we can get a green result instead of yellow "tests skipped" results that we would do by marking tests as skipped of the single/multisite condition was not correct.

- Mark one test as requiring multisite.
- Remove the other test, as it was causing an issue, and doesn't seem to be testing anything about CAP anyway.

- Make dynamic properties explicit.
- Skip a test that generates a deprecation notice in PHP 8.1 + WP < 6.3.

Highest and lowest versions of PHP 7, and PHP 8.
Highest and lowest versions of WP, plus trunk.

See https://make.wordpress.org/core/2021/09/27/changes-to-the-wordpress-core-php-test-suite/#integration-tests-ci-changes - PHPUnit 9 removed a `PHPUnit\Util\Getopt` class, but the [fix](https://core.trac.wordpress.org/changeset/51570/) wasn't applied to WP until 5.9.

Also - exclude WP 5.7 on PHP 8.2 since it is not supported.