fix: pin major and minor versions of MariaDB and MySQL

Releases of MariaDB and MySQL shouldn't be bumped blindly because of the
risk of breaking compatibility which might applications depending on
them prevent to work correctly.

renovate.json

@@ -23,6 +23,20 @@
         "minor",
         "patch"
       ]
+    },
+    {
+      "enabled": false,
+      "managers": [
+        "docker-compose",
+        "dockerfile"
+      ],
+      "matchUpdateTypes": [
+        "major",
+        "minor"
+      ],
+      "packagePatterns": [
+        "^([^/]+\\/)*(mariadb|mysql)(:.*)?$"
+      ]
     }
   ]
 }