minor #58094 Use Stringable whenever possible (fabpot)

This PR was merged into the 7.2 branch.

Discussion
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Use Stringable whenever possible

| Q             | A
| ------------- | ---
| Branch?       | 7.2
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Issues        | n/a
| License       | MIT

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Commits
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06b49968a5 Use Stringable whenever possible

Author: fabpot

Authorization/TraceableAccessDecisionManager.php

@@ -85,7 +85,7 @@ public function getStrategy(): string
         if (null === $this->strategy) {
             return '-';
         }
-        if (method_exists($this->strategy, '__toString')) {
+        if ($this->strategy instanceof \Stringable) {
             return (string) $this->strategy;
         }