Remove old laravel versions

Author: David Bohn

.github/workflows/main.yml

@@ -13,27 +13,12 @@ jobs:
     strategy:
       matrix:
         php: [7.4, 7.3, 7.2]
-        laravel: [6.*, 5.8.*, 5.7.*, 5.6.*, 5.5.*]
+        laravel: [6.*]
         dependency-version: [prefer-lowest, prefer-stable]
         os: [ubuntu-latest]
         include:
           - laravel: 6.*
             testbench: 4.*
-          - laravel: 5.8.*
-            testbench: 3.8.*
-          - laravel: 5.7.*
-            testbench: 3.7.*
-          - laravel: 5.6.*
-            testbench: 3.6.*
-          - laravel: 5.5.*
-            testbench: 3.5.*
-        exclude:
-          - laravel: 5.7.*
-            php: 7.4
-          - laravel: 5.6.*
-            php: 7.4
-          - laravel: 5.5.*
-            php: 7.4
 
     name: P${{ matrix.php }} - L${{ matrix.laravel }} - ${{ matrix.dependency-version }} - ${{ matrix.os }}