minor symfony#59476 [PhpUnitBridge] Mark AttributeReader as internal (HypeMC)

This PR was merged into the 7.3 branch.

Discussion
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[PhpUnitBridge] Mark `AttributeReader` as internal

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Follow-up to symfony#59384

Didn't notice this in my original PR, but it'd make sense for the `AttributeReader` class to be marked as internal.

Commits
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ba073c2 [PhpUnitBridge] Mark `AttributeReader` as internal

Author: chalasr

src/Symfony/Bridge/PhpUnit/Metadata/AttributeReader.php

@@ -12,6 +12,8 @@
 namespace Symfony\Bridge\PhpUnit\Metadata;
 
 /**
+ * @internal
+ *
  * @template T of object
  */
 final class AttributeReader