deps(deps-dev): update phpspec/prophecy-phpunit requirement

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@v2.3.0...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

@@ -37,7 +37,7 @@
         "friendsofphp/php-cs-fixer": "^3.75",
         "mikey179/vfsstream": "^1.6",
         "phpspec/prophecy": "^1.10",
-        "phpspec/prophecy-phpunit": "^2.3",
+        "phpspec/prophecy-phpunit": "^2.4",
         "phpunit/phpunit": "^7.5|^9.0|^10.0",
         "roave/security-advisories": "dev-master",
         "symfony/var-dumper": "^3.0|^4.0|^5.0|^6.0|^7.0"