This (small) change needs a little explaining....

First of all, the `setup-php` action, by default uses a "production"-type ini file. This means that `error_reporting` is set to `E_ALL & ~E_DEPRECATED & ~E_STRICT` and `display_errors` is set to `Off`.

For the purposes of CI, I'd recommend running with `-1` (always include all error levels on all PHP versions) and `display_errors=On` to ensure **all** PHP notices are shown.

This is now fixed by adding the `ini-values` setting to `setup-php`.

I've also made minor other tweaks to the `setup-php` config:
* `tools: composer` is not needed as Composer is installed by default.
* `extension: xdebug` is not the correct way to enable `xdebug` for code coverage. `coverage: xdebug` is (and is Xdebug cross-version compatible for Xdebug 2 and 3).

Second of all, a change was made in PHPUnit 8.5.21 and 9.5.10, which changes the default value of the PHPUnit `convertDeprecationsToExceptions` attribute from `true` to `false`, meaning that tests would no longer fail on deprecation notices.

Not great for open source packages which generally need to handle deprecations in a timely matter so as not to block other packages.

So adding the `convertDeprecationsToExceptions` attribute and explicitly setting the value to `true` brings back the old behaviour and will allow for failing the tests on deprecation notices.

Add PHP 8.2-8.4 to test matrix

…deprecation-notices

Tests: fail on deprecation notices