Build/Test Tools: Expose port 3306 of MySQL container.

This only defines the container port to allow `docker-compose` to choose an ephemeral host port.

Props ocean90, peterwilsoncc.
Fixes #48281.

git-svn-id: https://develop.svn.wordpress.org/trunk@47225 602fd350-edb4-49c9-b593-d223f7449a82

docker-compose.yml

@@ -58,6 +58,9 @@ services:
     networks:
       - wpdevnet
 
+    ports:
+      - "3306"
+
     environment:
       MYSQL_ROOT_PASSWORD: password