libpod/container_top_linux.c: fix missing header

As this file uses open it needs to include fcntl.h.
This should fix the build error seen on epel9[1], not sure why it works
on the other platforms.

[1] https://download.copr.fedorainfracloud.org/results/packit/containers-podman-23113/epel-9-aarch64/07672197-podman/builder-live.log.gz

Fixes 65ed96585d ("podman top: join the container userns")

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

libpod/container_top_linux.c

@@ -3,6 +3,7 @@
 
 #define _GNU_SOURCE
 #include <errno.h>
+#include <fcntl.h>
 #include <sched.h>
 #include <stdio.h>
 #include <stdlib.h>