Drop mysql 5.6 in CI

Author: bcardiff

.github/workflows/ci.yml

@@ -14,12 +14,8 @@ jobs:
       matrix:
         os: [ubuntu-latest]
         crystal: [1.3.0, latest, nightly]
-        mysql_version: ["5.6", "5.7"]
+        mysql_version: ["5.7"]
         database_host: ["default", "/tmp/mysql.sock"]
-        exclude:
-          # mysql 5.6 fails to run some specs using socket
-          - mysql_version: 5.6
-            database_host: /tmp/mysql.sock
     runs-on: ${{ matrix.os }}
     steps:
       - name: Install Crystal