fix: testbench version restrictions

Author: joostdebruijn

.github/workflows/tests.yml

@@ -14,6 +14,13 @@ jobs:
         php: [8.2, 8.1, 8.0]
         laravel: [10.*, 9.*, 8.*]
         stability: [prefer-lowest, prefer-stable]
+        include:
+          - laravel: 10.*
+            testbench: 8.*
+          - laravel: 9.*
+            testbench: 7.*
+          - laravel: 8.*
+            testbench: ^6.23
         exclude:
           - laravel: 10.*
             php: 8.0