etc: rename the temporary dirs so that they are recognisable

This makes it a lot easier to understand which dir is which

nixos/modules/system/etc/etc.nix

@@ -231,13 +231,13 @@ in
       if [[ ! $IN_NIXOS_SYSTEMD_STAGE1 ]] && [[ "${config.system.build.etc}/etc" != "$(readlink -f /run/current-system/etc)" ]]; then
         echo "remounting /etc..."
 
-        tmpMetadataMount=$(mktemp --directory)
+        tmpMetadataMount=$(mktemp --directory -t nixos-etc-metadata.XXXXXXXXXX)
         mount --type erofs ${config.system.build.etcMetadataImage} $tmpMetadataMount
 
         # Mount the new /etc overlay to a temporary private mount.
         # This needs the indirection via a private bind mount because you
         # cannot move shared mounts.
-        tmpEtcMount=$(mktemp --directory)
+        tmpEtcMount=$(mktemp --directory -t nixos-etc.XXXXXXXXXX)
         mount --bind --make-private $tmpEtcMount $tmpEtcMount
         mount --type overlay overlay \
           --options lowerdir=$tmpMetadataMount::${config.system.build.etcBasedir},${etcOverlayOptions} \