minor #17053 Update broken link of PHPUnit documentation (MrJavadAdib)

This PR was merged into the 5.4 branch.

Discussion
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Update broken link of PHPUnit documentation

update to doc v9.5

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Commits
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2dbdc43 Update broken link of PHPUnit documentation

Author: javiereguiluz

testing.rst

@@ -1017,12 +1017,12 @@ Learn more
 
 .. _`PHPUnit`: https://phpunit.de/
 .. _`documentation`: https://phpunit.readthedocs.io/
-.. _`Writing Tests for PHPUnit`: https://phpunit.readthedocs.io/en/stable/writing-tests-for-phpunit.html
-.. _`PHPUnit documentation`: https://phpunit.readthedocs.io/en/stable/configuration.html
+.. _`Writing Tests for PHPUnit`: https://phpunit.readthedocs.io/en/9.5/writing-tests-for-phpunit.html
+.. _`PHPUnit documentation`: https://phpunit.readthedocs.io/en/9.5/configuration.html
 .. _`unit test`: https://en.wikipedia.org/wiki/Unit_testing
 .. _`DAMADoctrineTestBundle`: https://github.com/dmaicher/doctrine-test-bundle
 .. _`Doctrine data fixtures`: https://symfony.com/doc/current/bundles/DoctrineFixturesBundle/index.html
 .. _`DoctrineFixturesBundle documentation`: https://symfony.com/doc/current/bundles/DoctrineFixturesBundle/index.html
 .. _`SymfonyMakerBundle`: https://symfony.com/doc/current/bundles/SymfonyMakerBundle/index.html
-.. _`PHPUnit Assertion`: https://phpunit.readthedocs.io/en/stable/assertions.html
+.. _`PHPUnit Assertion`: https://phpunit.readthedocs.io/en/9.5/assertions.html
 .. _`section 4.1.18 of RFC 3875`: https://tools.ietf.org/html/rfc3875#section-4.1.18