[BUGFIX] Avoid unsetting almost all PHP-CS-Fixes rules

Followup to #1533

.php-cs-fixer.php

@@ -4,15 +4,15 @@
 use TYPO3\CodingStandards\CsFixerConfig;
 
 $config = CsFixerConfig::create();
+
 // This is required as long as we are on PHPUnit 9.x. It can be removed after the switch to PHPUnit 10.x.
 // @see https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/issues/8337
-$config->setRules(
-    [
-        'php_unit_test_case_static_method_calls' => ['call_type' => 'self', 'methods' => ['createStub' => 'this']],
-    ]
-);
+$rules = $config->getRules();
+$rules['php_unit_test_case_static_method_calls'] = ['call_type' => 'self', 'methods' => ['createStub' => 'this']];
+$config->setRules($rules);
 
 // @TODO 4.0 no need to call this manually
 $config->setParallelConfig(ParallelConfigFactory::detect());
+
 $config->getFinder()->in('Classes')->in('Configuration')->in('Tests');
 return $config;