install-darwin: track mount permission edge-case fix

Same as 1fd127a068, but applied to a
code path (volume_pass_works -> verify_volume_pass) that the reporting
user didn't hit and wasn't able to trigger manually. I am not certain
but I suspect it will be easier to add prophylactically than to debug
if its absence causes trouble some day.

scripts/create-darwin-volume.sh

@@ -246,6 +246,7 @@ get_volume_pass() {
 verify_volume_pass() {
     local volume_special="$1" # (i.e., disk1s7)
     local volume_uuid="$2"
+    _sudo "to confirm the password actually unlocks the volume" \
         /usr/sbin/diskutil apfs unlockVolume "$volume_special" -verify -stdinpassphrase -user "$volume_uuid"
 }