Reduce test matrix combinations in CI

Author: lam0819

.github/workflows/run-tests.yml

@@ -19,8 +19,13 @@ jobs:
         os: [ubuntu-latest]
         php: [8.4, 8.3]
         laravel: [12.*, 11.*]
-        stability: [prefer-lowest, prefer-stable]
+        stability: [prefer-stable]
         include:
+          # Keep one lowest-deps lane to validate minimum compatibility.
+          - php: 8.3
+            laravel: 11.*
+            stability: prefer-lowest
+            testbench: 9.*
           - laravel: 12.*
             testbench: 10.*
           - laravel: 11.*