Update phpspec/prophecy-phpunit requirement from ^2.1 to ^2.4

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@v2.1.0...v2.4.0)

---
updated-dependencies:
- dependency-name: phpspec/prophecy-phpunit
  dependency-version: 2.4.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

composer.json

@@ -63,7 +63,7 @@
         "nyholm/psr7": "^1.8",
         "nyholm/psr7-server": "^1.1",
         "phpspec/prophecy": "^1.19",
-        "phpspec/prophecy-phpunit": "^2.1",
+        "phpspec/prophecy-phpunit": "^2.4",
         "phpstan/phpstan": "^1.12",
         "phpunit/phpunit": "^9.6",
         "slim/http": "^1.3",