Update orchestra/testbench requirement from ^8.19 to ^8.20

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/develop/CHANGELOG-8.x.md)
- [Commits](orchestral/testbench@v8.19.0...v8.20.0)

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

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

composer.json

@@ -36,7 +36,7 @@
         "nunomaduro/larastan": "^2.8",
         "laravel/pint": "^1.13",
         "nunomaduro/collision": "^6.4.0",
-        "orchestra/testbench": "^8.19",
+        "orchestra/testbench": "^8.20",
         "pestphp/pest-plugin-laravel": "^v1.4",
         "pestphp/pest-plugin-parallel": "^1.2",
         "phpmd/phpmd": "^2.15",