Update phpunit/phpunit requirement from 9.6.7 to 9.6.10

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/9.6.10/ChangeLog-9.6.md)
- [Commits](sebastianbergmann/phpunit@9.6.7...9.6.10)

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

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

composer.json

@@ -19,7 +19,7 @@
   "require-dev": {
     "dms/phpunit-arraysubset-asserts": "0.5.0",
     "friendsofphp/php-cs-fixer": "*",
-    "phpunit/phpunit": "9.6.7",
+    "phpunit/phpunit": "9.6.10",
     "php-coveralls/php-coveralls": "2.5.3",
     "squizlabs/php_codesniffer": "3.7.2"
   },