git_connect: use use_shell instead of explicit "sh", "-c"

This is a followup to ac0ba18d (run-command: convert simple callsites to
use_shell, 2009-12-30), for consistency.
Signed-off-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

connect.c

@@ -613,8 +613,7 @@ struct child_process *git_connect(int fd[2], const char *url_orig,
 			NULL
 		};
 		conn->env = env;
-		*arg++ = "sh";
-		*arg++ = "-c";
+		conn->use_shell = 1;
 	}
 	*arg++ = cmd.buf;
 	*arg = NULL;