Update nyholm/psr7 requirement from ^1.2 to ^1.4

Updates the requirements on [nyholm/psr7](https://github.com/Nyholm/psr7) to permit the latest version.
- [Release notes](https://github.com/Nyholm/psr7/releases)
- [Changelog](https://github.com/Nyholm/psr7/blob/master/CHANGELOG.md)
- [Commits](Nyholm/psr7@1.2.0...1.4.0)

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

composer.json

@@ -33,7 +33,7 @@
     "require-dev": {
         "cdn77/coding-standard": "^5.0",
         "infection/infection": "^0.20.1",
-        "nyholm/psr7": "^1.2",
+        "nyholm/psr7": "^1.4",
         "php-http/curl-client": "^2.1",
         "phpstan/extension-installer": "^1.0",
         "phpstan/phpstan": "0.12.81",