ci: Test against PHP 8.3

It's released, let's start testing against it.

.github/files/generate-ci-matrix.php

@@ -58,7 +58,7 @@
 $matrix = array();
 
 // Add PHP tests.
-foreach ( array( '7.0', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2' ) as $php ) {
+foreach ( array( '7.0', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3' ) as $php ) {
 	$matrix[] = array(
 		'name'    => "PHP tests: PHP $php WP latest",
 		'script'  => 'test-php',

.github/versions.sh

@@ -6,4 +6,4 @@ PNPM_VERSION=8.6.8
 
 # Other useful version numbers.
 MIN_PHP_VERSION=7.0
-MAX_PHP_VERSION=8.2
+MAX_PHP_VERSION=8.3

.github/workflows/linting.yml

@@ -171,7 +171,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-versions: [ '7.0', '7.2', '7.4', '8.0', '8.1', '8.2' ]
+        php-versions: [ '7.0', '7.2', '7.4', '8.0', '8.1', '8.2', '8.3' ]
         experimental: [ false ]
 
     steps:

docs/monorepo.md

@@ -42,7 +42,7 @@ All GitHub Actions configuration for the monorepo, including CI, lives in `.gith
 
 ## Compatibility
 
-All projects should be compatible with PHP versions WordPress supports. That's currently PHP 7.0 to 8.2.
+All projects should be compatible with PHP versions WordPress supports. That's currently PHP 7.0 to 8.3.
 
 ## First Time
 
@@ -210,15 +210,15 @@ If a project contains PHP tests (typically PHPUnit), it must define `.scripts.te
 
 A MySQL database is available if needed; credentials may be found in `~/.my.cnf`. Note that the host must be specified as `127.0.0.1`, as when passed `localhost` PHP will try to connect via a Unix domain socket which is not available in the Actions environment.
 
-Tests are run with a variety of supported PHP versions from 7.0 to 8.2. If you have tests that only need to be run once, run them when `PHP_VERSION` matches that in `.github/versions.sh`.
+Tests are run with a variety of supported PHP versions from 7.0 to 8.3. If you have tests that only need to be run once, run them when `PHP_VERSION` matches that in `.github/versions.sh`.
 
 #### PHP tests for non-plugins
 
 For all project types other than WordPress plugins, the necessary version of PHPUnit and/or any other tools should be pulled in via Composer.
 
 We currently make use of the following packages in testing; it's encouraged to use these rather than introducing other tools that serve the same purpose.
 
-* [yoast/phpunit-polyfills](https://packagist.org/packages/yoast/phpunit-polyfills) supplies polyfills for compatibility with PHPUnit 6.5 to 9.0, to support PHP 7.0 to 8.2.
+* [yoast/phpunit-polyfills](https://packagist.org/packages/yoast/phpunit-polyfills) supplies polyfills for compatibility with PHPUnit 6.5 to 9.0, to support PHP 7.0 to 8.3.
   * Do not use `Yoast\PHPUnitPolyfills\TestCases\TestCase` or `Yoast\PHPUnitPolyfills\TestCases\XTestCase`. Just use the `@before`, `@after`, `@beforeClass`, and `@afterClass` annotations directly.
 * PHPUnit's built-in mocking is used for class mocks.
 * [brain/monkey](https://packagist.org/packages/brain/monkey) is used for mocking functions, and can also provide some functions for minimal WordPress compatibility.