Change mysql for 5.6 version

Author: Rahe

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.operating-system }}
     services:
       mysql:
-        image: mysql:5.7
+        image: mysql:5.6
         env:
           MYSQL_ALLOW_EMPTY_PASSWORD: false
           MYSQL_ROOT_PASSWORD: root