update testing matrix

Author: duncanmcclean

.github/workflows/tests.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       matrix:
         php: [8.3, 8.4, 8.5]
-        laravel: [12.*]
+        laravel: [12.*, 13.*]
         stability: [prefer-lowest, prefer-stable]
 
     name: P${{ matrix.php }} - L${{ matrix.laravel }} - ${{ matrix.stability }}