Bump phpunit/phpunit from 7.5.20 to 9.5.4

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 7.5.20 to 9.5.4.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-9.5.md)
- [Commits](sebastianbergmann/phpunit@7.5.20...9.5.4)

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

composer.json

@@ -155,7 +155,7 @@
         "npm-asset/yarn": "1.21.1",
         "oomphinc/composer-installers-extender": "^2.0",
         "php-http/guzzle6-adapter": "^1.1",
-        "phpunit/phpunit": "^7",
+        "phpunit/phpunit": "^9",
         "querypath/querypath": "^3.0",
         "simplesamlphp/simplesamlphp": "^1.18",
         "squizlabs/php_codesniffer": "^3.5",