fix: unclosed socket warning in db containers (testcontainers#378)

This PR fixes testcontainers#379

Author: sha1n

core/testcontainers/core/generic.py

@@ -36,7 +36,10 @@ def _connect(self) -> None:
         import sqlalchemy
 
         engine = sqlalchemy.create_engine(self.get_connection_url())
-        engine.connect()
+        try:
+            engine.connect()
+        finally:
+            engine.dispose()
 
     def get_connection_url(self) -> str:
         raise NotImplementedError