minor #39775 [WIP] Use ::class keyword when possible (fabpot)

This PR was merged into the 4.4 branch.

Discussion
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[WIP] Use ::class keyword when possible

| Q             | A
| ------------- | ---
| Branch?       | 4.4 <!-- see below -->
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | n/a  <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT
| Doc PR        | n/a

Commits
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036a36cb14 Use ::class keyword when possible

Author: fabpot

Tests/Controller/ArgumentResolverTest.php

@@ -132,7 +132,7 @@ public function testGetArgumentsFailsOnUnresolvedValue()
             self::$resolver->getArguments($request, $controller);
             $this->fail('->getArguments() throws a \RuntimeException exception if it cannot determine the argument value');
         } catch (\Exception $e) {
-            $this->assertInstanceOf('\RuntimeException', $e, '->getArguments() throws a \RuntimeException exception if it cannot determine the argument value');
+            $this->assertInstanceOf(\RuntimeException::class, $e, '->getArguments() throws a \RuntimeException exception if it cannot determine the argument value');
         }
     }