better CI for lower/upper bounds between cakephp versions

Author: cnizzardini

.github/workflows/pull-request.yml

@@ -124,7 +124,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        version: ['~5.0', '~5.1']
+        version: ['~5.0.0', '^5.0']
     steps:
       - name: Checkout
         uses: actions/checkout@v2