Disable suid and atime on the /nix mount point on Darwin

The Determinate Nix Installer has set nosuid and noatime in DeterminateSystems/nix-installer#1338, and figured this perf and security improvement is worthy of upstreaming.

The /nix volume shouldn't have setuid binaries anyway, and filesystems seem to generally be noatime on macOS.
Further, the garbage collector doesn't use atime.

(cherry picked from commit 4137ead)

scripts/create-darwin-volume.sh

@@ -463,7 +463,7 @@ EOF
 
     EDITOR="$SCRATCH/ex_cleanroom_wrapper" _sudo "to add nix to fstab" "$@" <<EOF
 :a
-UUID=$uuid $escaped_mountpoint apfs rw,noauto,nobrowse,suid,owners
+UUID=$uuid $escaped_mountpoint apfs rw,noauto,nobrowse,nosuid,noatime,owners
 .
 :x
 EOF