minor #26982 [Cache] Add missing @internal tag on ProxyTrait (nicolas-grekas)

This PR was merged into the 3.4 branch.

Discussion
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[Cache] Add missing `@internal` tag on ProxyTrait

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

All traits in Cache are internal. We just forgot the annotation on this one.

Commits
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3d7c7cf39a [Cache] Add missing `@internal` tag on ProxyTrait

src/Symfony/Component/Cache/Traits/ProxyTrait.php

@@ -16,6 +16,8 @@ use Symfony\Component\Cache\ResettableInterface;
 
 /**
  * @author Nicolas Grekas <p@tchwork.com>
+ *
+ * @internal
  */
 trait ProxyTrait
 {