Ensure /etc isn't writable by group

[sjpb]

munged checks on startup that the path to its key is secure.

Because Rocky-9-GenericCloud-Base-9.4-20240523.0.x86_64.qcow2 changed the permissions on /etc this image fails with:

munged: Error: Keyfile is insecure: group-writable permissions without sticky bit set on "/etc"

Permissions comparison:

# Rocky-9-GenericCloud-Base-9.3-20231113.0.x86_64.qcow2
[rocky@sb-rl9-3 ~]$ ls -ld /etc/
drwxr-xr-x. 93 root root 8192 Jun  5 14:54 /etc/

# Rocky-9-GenericCloud-Base-9.4-20240523.0.x86_64.qcow2
[rocky@sb-rl9-4 ~]$ ls -ld /etc/
drwxrwxr-x. 88 root root 8192 Jun  5 14:54 /etc/

[sjpb]

@m-bull I've asked: https://forums.rockylinux.org/t/changed-permissions-on-etc-in-rl9-4-genericcloud-image/14449