Update guzzlehttp/psr7 requirement from ^2.5 to ^2.6

Updates the requirements on [guzzlehttp/psr7](https://github.com/guzzle/psr7) to permit the latest version.
- [Release notes](https://github.com/guzzle/psr7/releases)
- [Changelog](https://github.com/guzzle/psr7/blob/2.6/CHANGELOG.md)
- [Commits](guzzle/psr7@2.5.0...2.6.1)

---
updated-dependencies:
- dependency-name: guzzlehttp/psr7
  dependency-type: direct:development
...

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

composer.json

@@ -56,7 +56,7 @@
     "require-dev": {
         "ext-simplexml": "*",
         "adriansuter/php-autoload-override": "^1.4",
-        "guzzlehttp/psr7": "^2.5",
+        "guzzlehttp/psr7": "^2.6",
         "httpsoft/http-message": "^1.1",
         "httpsoft/http-server-request": "^1.1",
         "laminas/laminas-diactoros": "^2.17",