Update run-tests.yml

Author: barryvdh

.github/workflows/run-tests.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   php-tests:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     timeout-minutes: 15
     env:
       COMPOSER_NO_INTERACTION: 1