Update psr/http-message requirement from ^1.1 to ^2.0

Updates the requirements on [psr/http-message](https://github.com/php-fig/http-message) to permit the latest version.
- [Release notes](https://github.com/php-fig/http-message/releases)
- [Changelog](https://github.com/php-fig/http-message/blob/master/CHANGELOG.md)
- [Commits](php-fig/http-message@1.1...2.0)

---
updated-dependencies:
- dependency-name: psr/http-message
  dependency-type: direct:production
...

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

composer.json

@@ -19,7 +19,7 @@
     ],
     "require": {
         "php": "^7.4 || ^8.0",
-        "psr/http-message": "^1.1",
+        "psr/http-message": "^2.0",
         "slim/slim": "^4.12",
         "twig/twig": "^3.8",
         "symfony/polyfill-php81": "^1.29"