Test only stable

Author: Holger Lösken

.github/workflows/tests.yml

@@ -7,7 +7,7 @@ jobs:
       matrix:
         php: ['7.3', '7.4', '8.0']
         laravel: [6.*, 7.*, 8.*]
-        dependency-version: [prefer-lowest, prefer-stable]
+        dependency-version: [prefer-stable]
         include:
           - laravel: 8.*
             testbench: 6.*