Upgrade PHPUnit to 9.4 (#443)

Author: villfa

Makefile

@@ -44,7 +44,7 @@ cs-check: $(CODE_SNIFFER)
 	$(PHPNOGC) $(CODE_SNIFFER)
 
 .PHONY: phpstan
-PHPSTAN=bin/phpstan
+PHPSTAN=vendor-bin/phpstan/vendor/bin/phpstan
 phpstan: ## Runs PHPStan
 phpstan: $(PHPSTAN)
 	$(PHPNOGC) $(PHPSTAN) analyze src --level max

composer.json

@@ -31,7 +31,8 @@
     "require-dev": {
         "bamarni/composer-bin-plugin": "^1.1",
         "humbug/box": "^3.8",
-        "phpunit/phpunit": "^8.0"
+        "phpspec/prophecy-phpunit": "^2.0",
+        "phpunit/phpunit": "^9.0"
     },
     "replace": {
         "humbug/php-scoper": "self.version"