Update nyholm/psr7 requirement from ^1.3 to ^1.5

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@1.3.0...1.5.1)

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

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

Author: dependabot[bot]

composer.json

@@ -79,7 +79,7 @@
         "ekino/phpstan-banned-code": "^1.0",
         "infection/infection": "^0.26",
         "matthiasnoback/symfony-config-test": "^4.3.0",
-        "nyholm/psr7": "^1.3",
+        "nyholm/psr7": "^1.5",
         "php-http/mock-client": "^1.0",
         "php-parallel-lint/php-parallel-lint": "^1.3",
         "phpbench/phpbench": "^1.2",