tests/kola: use toolbox container image for selinux.podman-tmpfs-context

In F40 the base container no longer includes `util-linux-core` so we
can't run the `mount` command. Let's just pull the toolbox container for
now, which does include it.

tests/kola/selinux/podman-tmpfs-context

@@ -15,7 +15,7 @@ set -xeuo pipefail
 # shellcheck disable=SC1091
 . "$KOLA_EXT_DATA/commonlib.sh"
 
-context=$(podman run --rm --privileged quay.io/fedora/fedora:40 \
+context=$(podman run --rm --privileged quay.io/fedora/fedora-toolbox:40 \
             bash -c "mount -t tmpfs tmpfs /mnt/ && stat --format '%C' /mnt/")
 if [ "$context" != "system_u:object_r:container_file_t:s0" ]; then
     fatal "SELinux context for files on a tmpfs inside a container is wrong"