composer(deps-dev): Update symfony/phpunit-bridge requirement

Updates the requirements on [symfony/phpunit-bridge](https://github.com/symfony/phpunit-bridge) to permit the latest version.
- [Release notes](https://github.com/symfony/phpunit-bridge/releases)
- [Changelog](https://github.com/symfony/phpunit-bridge/blob/6.3/CHANGELOG.md)
- [Commits](symfony/phpunit-bridge@v6.3.6...v6.3.8)

---
updated-dependencies:
- dependency-name: symfony/phpunit-bridge
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -21,7 +21,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^9.6.13",
-        "symfony/phpunit-bridge": "^6.3.6"
+        "symfony/phpunit-bridge": "^6.3.8"
     },
     "autoload": {
         "psr-4": {