Update orchestra/testbench requirement from ^6.28|^7.0 to ^7.6.0

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/7.x/CHANGELOG-7.x.md)
- [Commits](https://github.com/orchestral/testbench/commits/v7.6.0)

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

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

Author: dependabot[bot]

composer.json

@@ -45,7 +45,7 @@
     },
     "require-dev": {
         "mockery/mockery": "^1.5",
-        "orchestra/testbench": "^6.28|^7.0",
+        "orchestra/testbench": "^7.6.0",
         "orchestra/testbench-core": "^6.28|^7.0",
         "phpunit/phpunit": "^9.5.20"
     },