Update orchestra/testbench requirement from ^5.0 to ^5.0 || ^6.0

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/6.x/CHANGELOG-6.x.md)
- [Commits](orchestral/testbench@v5.0.0...v6.0.0)

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

Author: dependabot-preview[bot]

composer.json

@@ -34,7 +34,7 @@
     },
     "require-dev": {
         "consistence/coding-standard": "3.10.1",
-        "orchestra/testbench": "^5.0",
+        "orchestra/testbench": "^5.0 || ^6.0",
         "phpmd/phpmd": "^2.6",
         "phpunit/phpunit": "9.*",
         "slevomat/coding-standard": "6.0.8",