Update phpspec/prophecy requirement from ^1.19 to ^1.20

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@v1.19.0...v1.20.0)

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

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

Author: dependabot[bot]

composer.json

@@ -40,7 +40,7 @@
     "adriansuter/php-autoload-override": "^1.4",
     "http-interop/http-factory-tests": "^1.1.0",
     "php-http/psr7-integration-tests": "1.3.0",
-    "phpspec/prophecy": "^1.19",
+    "phpspec/prophecy": "^1.20",
     "phpspec/prophecy-phpunit": "^2.2",
     "phpstan/phpstan": "^1.11",
     "phpunit/phpunit": "^9.6",