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

This PR was merged into the 4.4 branch.

Discussion
----------

[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
-------

036a36cb14 Use ::class keyword when possible

Author: fabpot

Tests/Functional/UserPasswordEncoderCommandTest.php

@@ -258,7 +258,7 @@ public function testEncodePasswordSodiumOutput()
 
     public function testEncodePasswordNoConfigForGivenUserClass()
     {
-        $this->expectException('\RuntimeException');
+        $this->expectException(\RuntimeException::class);
         $this->expectExceptionMessage('No encoder has been configured for account "Foo\Bar\User".');
 
         $this->passwordEncoderCommandTester->execute([