minor #25577 [Bridge/PhpUnit] thank phpunit/phpunit (nicolas-grekas)

This PR was merged into the 3.3 branch.

Discussion
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[Bridge/PhpUnit] thank phpunit/phpunit

| Q             | A
| ------------- | ---
| Branch?       | 3.3
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
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c84c928 [Bridge/PhpUnit] thank phpunit/phpunit

src/Symfony/Bridge/PhpUnit/composer.json

@@ -41,6 +41,10 @@
     "extra": {
         "branch-alias": {
             "dev-master": "3.3-dev"
+        },
+        "thanks": {
+            "name": "phpunit/phpunit",
+            "url": "https://github.com/sebastianbergmann/phpunit"
         }
     }
 }