Change fmask value in /etc/fstab

[Tiagoquix]

Since #4506 we set fmask=0077,dmask=0077 by default to prevent bootctl being angry because the random-seed is world-acessible.

However, fmask=0177 probably makes more sense (dmask is fine not to change), and is also what systemd uses.

See:

• https://wiki.archlinux.org/title/Talk:EFI_system_partition#Mountpoint_umask
  • [3] from that: https://github.com/systemd/systemd/blob/32ac7af7888bc46f91c1af7d9ba05fec929b31ad/src/shared/dissect-image.c#L2366

[Tiagoquix]

CC @0xdeadd