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

@@ -23,7 +23,7 @@
     ],
     "require": {
         "php": "^7.2 || ^8.0",
-        "dealerdirect/phpcodesniffer-composer-installer": "^0.6.2 || ^0.7",
+        "dealerdirect/phpcodesniffer-composer-installer": "^0.6.2 || ^0.7 || ^1.0.0",
         "slevomat/coding-standard": "^8.6.2",
         "squizlabs/php_codesniffer": "^3.7"
     },