minor #5612 DX: use ::class whenever possible (kubawerlos)

This PR was squashed before being merged into the 2.18 branch.

Discussion
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DX: use ::class whenever possible

Commits
-------

c75d8e8d7 DX: use ::class whenever possible

phpstan.neon

@@ -59,5 +59,8 @@ parameters:
         -
             message: '/^\$this\(PhpCsFixer\\Tokenizer\\Tokens\) does not accept PhpCsFixer\\Tokenizer\\Token\|null\.$/'
             path: src/Tokenizer/Tokens.php
+        -
+            message: '/^Class Test\dConfig not found.$/'
+            path: tests/Console/ConfigurationResolverTest.php
 
     tipsOfTheDay: false

tests/Console/ConfigurationResolverTest.php

@@ -205,7 +205,7 @@ final class ConfigurationResolverTest extends TestCase
         $resolver = $this->createConfigurationResolver(['path' => [$dir.\DIRECTORY_SEPARATOR.'foo.php']]);
 
         static::assertSame($dir.\DIRECTORY_SEPARATOR.'.php_cs.dist', $resolver->getConfigFile());
-        static::assertInstanceOf('Test1Config', $resolver->getConfig());
+        static::assertInstanceOf(\Test1Config::class, $resolver->getConfig());
     }
 
     public function testResolveConfigFileSpecified()
@@ -215,7 +215,7 @@ final class ConfigurationResolverTest extends TestCase
         $resolver = $this->createConfigurationResolver(['config' => $file]);
 
         static::assertSame($file, $resolver->getConfigFile());
-        static::assertInstanceOf('Test4Config', $resolver->getConfig());
+        static::assertInstanceOf(\Test4Config::class, $resolver->getConfig());
     }
 
     /**