fix: Close docker client when stopping the docker container (#380)

Fixes the following warning

```
sys:1: ResourceWarning: unclosed <socket.socket fd=7, family=AddressFamily.AF_UNIX, type=SocketKind.SOCK_STREAM, proto=0, raddr=/Users/rodrigo/.docker/run/docker.sock>
```
 Related to #379

Co-authored-by: David Ankin <daveankin@gmail.com>

Author: rodrigoscc

core/testcontainers/core/container.py

@@ -76,6 +76,7 @@ def start(self) -> "DockerContainer":
 
     def stop(self, force=True, delete_volume=True) -> None:
         self._container.remove(force=force, v=delete_volume)
+        self.get_docker_client().client.close()
 
     def __enter__(self) -> "DockerContainer":
         return self.start()