minor #18965 [Testing] Update PHPUnit docs links (cba85)

This PR was merged into the 6.3 branch.

Discussion
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[Testing] Update PHPUnit docs links

Update all PHPUnit links of "Testing" page from `9.6` to `10.3`

Commits
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cb975e5 Update PHPUnit docs links

Author: javiereguiluz

testing.rst

@@ -1131,12 +1131,12 @@ Learn more
 
 .. _`PHPUnit`: https://phpunit.de/
 .. _`documentation`: https://docs.phpunit.de/
-.. _`Writing Tests for PHPUnit`: https://docs.phpunit.de/en/9.6/writing-tests-for-phpunit.html
-.. _`PHPUnit documentation`: https://docs.phpunit.de/en/9.6/configuration.html
+.. _`Writing Tests for PHPUnit`: https://docs.phpunit.de/en/10.3/writing-tests-for-phpunit.html
+.. _`PHPUnit documentation`: https://docs.phpunit.de/en/10.3/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://docs.phpunit.de/en/9.6/assertions.html
+.. _`PHPUnit Assertion`: https://docs.phpunit.de/en/10.3/assertions.html
 .. _`section 4.1.18 of RFC 3875`: https://tools.ietf.org/html/rfc3875#section-4.1.18