ci(php-dev): update orchestra/testbench requirement from ^8.0 to ^9.1

Updates the requirements on [orchestra/testbench](https://github.com/orchestral/testbench) to permit the latest version.
- [Release notes](https://github.com/orchestral/testbench/releases)
- [Changelog](https://github.com/orchestral/testbench/blob/9.x/CHANGELOG-9.x.md)
- [Commits](orchestral/testbench@v8.0.0...v9.1.2)

---
updated-dependencies:
- dependency-name: orchestra/testbench
  dependency-type: direct:development
...

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

composer.json

@@ -34,7 +34,7 @@
         "laravel/pint": "^1.0",
         "nunomaduro/collision": "^7.9",
         "nunomaduro/larastan": "^2.0",
-        "orchestra/testbench": "^8.0",
+        "orchestra/testbench": "^9.1",
         "pestphp/pest": "^2.1",
         "pestphp/pest-plugin-arch": "^2.0",
         "pestphp/pest-plugin-laravel": "^2.0",