Update phpspec/prophecy requirement from ^1.17 to ^1.18

Updates the requirements on [phpspec/prophecy](https://github.com/phpspec/prophecy) to permit the latest version.
- [Release notes](https://github.com/phpspec/prophecy/releases)
- [Changelog](https://github.com/phpspec/prophecy/blob/master/CHANGES.md)
- [Commits](phpspec/prophecy@v1.17.0...v1.18.0)

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

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

composer.json

@@ -23,7 +23,7 @@
         "psr/http-server-middleware": "^1.0"
     },
     "require-dev": {
-        "phpspec/prophecy": "^1.17",
+        "phpspec/prophecy": "^1.18",
         "phpspec/prophecy-phpunit": "^2.0",
         "phpunit/phpunit": "^9.6",
         "squizlabs/php_codesniffer": "^3.7"