Composer: allow for the 1.0.0 version of the Composer PHPCS plugin

The Composer PHPCS plugin has released its 1.0.0 version. 🎉

Important:
I've _widened_ the version constraints for the plugin, instead of _bumping_ it.

The reason for this is to prevent conflicts with end-user projects/other external PHPCS standards which may also require(-dev) the plugin, but may not (yet) have updated _their_ constraints for the plugin.
If the version would have been bumped instead of widened, those users would get an unsolvable conflict during the `composer install` run (unless they `require-dev` the plugin for the root project, but then, that's exactly what we _don't_ want them to do as external standards managing the versions of the plugins should  be more reliable).

Ref: https://github.com/PHPCSStandards/composer-installer/releases/tag/v1.0.0

composer.json

@@ -17,7 +17,7 @@
 	},
 	"require": {
 		"php": "^7.2 || ^8.0",
-		"dealerdirect/phpcodesniffer-composer-installer": "^0.6.2 || ^0.7",
+		"dealerdirect/phpcodesniffer-composer-installer": "^0.6.2 || ^0.7 || ^1.0",
 		"phpstan/phpdoc-parser": ">=1.15.2 <1.16.0",
 		"squizlabs/php_codesniffer": "^3.7.1"
 	},