CI: Small cleanup in the github actions workflow file
CI: Small cleanup in the github actions workflow file

Strengthen the container security settings, since we don't seem to
need more. The rest of the patch is cosmectic.

Signed-off-by: Frederic Barrat <c90240987c583ac0802fbeb88cb1684edc683e18@linux.ibm.com>
Signed-off-by: Cédric Le Goater <2d8cace2254d4e43578d21933db015d84bcc468a@kaod.org>

open-power/skiboot,qemu/skiboot,open-power/skiboot,legoater/skiboot,shenki/skiboot,open-power/skiboot,qemu/skiboot,qemu/skiboot,qemu/skiboot,legoater/skiboot,shenki/skiboot,legoater/skiboot,shenki/skiboot,shenki/skiboot,open-power/skiboot,legoater/skiboot,legoater/skiboot,shenki/skiboot,qemu/skiboot,open-power/skiboot