fix: Use datajoint/mysql image for testcontainers (has SSL configured)

The official mysql:8.0 image doesn't have SSL certificates configured,
causing SSL tests to fail. The datajoint/mysql:8.0 image has SSL
properly configured with certificates in /mysql_keys/.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

tests/conftest.py

@@ -114,7 +114,7 @@ def mysql_container():
     from testcontainers.mysql import MySqlContainer
 
     container = MySqlContainer(
-        image="mysql:8.0",
+        image="datajoint/mysql:8.0",  # Use datajoint image which has SSL configured
         username="root",
         password="password",
         dbname="test",