Fix return type for SSHClientConnection.create_process()

The create_process() call in SSHClientConnection had an incomplete
return type of SSHClientProcess, when it really should have been
SSHClientProcess[AnyStr] to match the AnyStr appearing in the
"input" argument. Thanks go to Matthew Bradbury for reporting
this issue.

asyncssh/connection.py

@@ -4061,7 +4061,7 @@ async def create_process(self, *args: object,
                              stderr: ProcessTarget = PIPE,
                              bufsize: int = io.DEFAULT_BUFFER_SIZE,
                              send_eof: bool = True, recv_eof: bool = True,
-                             **kwargs: object) -> SSHClientProcess:
+                             **kwargs: object) -> SSHClientProcess[AnyStr]:
         """Create a process on the remote system
 
            This method is a coroutine wrapper around :meth:`create_session`