Bump phpunit/phpunit from 8.5.38 to 9.6.19

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 8.5.38 to 9.6.19.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/9.6.19/ChangeLog-9.6.md)
- [Commits](sebastianbergmann/phpunit@8.5.38...9.6.19)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

composer.json

@@ -25,7 +25,7 @@
     },
     "require-dev": {
         "mediawiki/minus-x": "^1.0",
-        "phpunit/phpunit": "^7.0|^8.0",
+        "phpunit/phpunit": "^9.6.19",
         "symfony/var-dumper": "^5|^6|^7",
         "opsway/psr12-strict-coding-standard": "^1"
     },