Update phpspec/prophecy-phpunit requirement from ^2.0 to ^2.1

Updates the requirements on [phpspec/prophecy-phpunit](https://github.com/phpspec/prophecy-phpunit) to permit the latest version.
- [Release notes](https://github.com/phpspec/prophecy-phpunit/releases)
- [Changelog](https://github.com/phpspec/prophecy-phpunit/blob/master/CHANGES.md)
- [Commits](phpspec/prophecy-phpunit@v2.0.0...v2.1.0)

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

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

composer.json

@@ -26,7 +26,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^9.6",
-        "phpspec/prophecy-phpunit": "^2.0",
+        "phpspec/prophecy-phpunit": "^2.1",
         "phpstan/phpstan": "^1.10.46",
         "psr/http-factory": "^1.0",
         "squizlabs/php_codesniffer": "^3.7"