Update php-http/mock-client requirement from ^1.0 to ^1.5

Updates the requirements on [php-http/mock-client](https://github.com/php-http/mock-client) to permit the latest version.
- [Release notes](https://github.com/php-http/mock-client/releases)
- [Changelog](https://github.com/php-http/mock-client/blob/master/CHANGELOG.md)
- [Commits](php-http/mock-client@1.0.0...1.5.0)

---
updated-dependencies:
- dependency-name: php-http/mock-client
  dependency-type: direct:development
...

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

Author: dependabot[bot]

composer.json

@@ -80,7 +80,7 @@
         "infection/infection": "^0.26",
         "matthiasnoback/symfony-config-test": "^4.3.0",
         "nyholm/psr7": "^1.5",
-        "php-http/mock-client": "^1.0",
+        "php-http/mock-client": "^1.5",
         "php-parallel-lint/php-parallel-lint": "^1.3",
         "phpbench/phpbench": "^1.2",
         "phpstan/extension-installer": "^1.1",