Bump PHPCompatibility to current dev version

We are using version 9.3.5 that is from December 2019. Since
then lots of new sniffs and compatibility with PHP 8.x versions
has been provided.

So, while it's not nice to use a dev version, let's stick to
current one (dev-develop#2fb82334) and see how things go.

composer.json

@@ -16,8 +16,8 @@
     ],
     "require": {
         "dealerdirect/phpcodesniffer-composer-installer": "^0.7.2",
-        "squizlabs/php_codesniffer": "^3.6",
-        "phpcompatibility/php-compatibility": "^9.3"
+        "squizlabs/php_codesniffer": "^3.7.1",
+        "phpcompatibility/php-compatibility": "dev-develop#2fb82334"
     },
     "config": {
         "allow-plugins": {