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/Store/ExpiringStoreTestTrait.php

@@ -60,7 +60,7 @@ public function testExpiration()
      */
     public function testAbortAfterExpiration()
     {
-        $this->expectException('\Symfony\Component\Lock\Exception\LockExpiredException');
+        $this->expectException(LockExpiredException::class);
         $key = new Key(uniqid(__METHOD__, true));
 
         /** @var PersistingStoreInterface $store */