test: update postmortem metadata test

This commit updates the following postmortem metadata constant:

- v8dbg_bit_field3_dictionary_map_shift
  - This is now v8dbg_bit_field3_is_dictionary_map_shift as of
    https://github.com/v8/v8/commit/7a159da151e5f5437d6924de4fd142f854d3df4e

Refs: https://github.com/nodejs/node-v8/pull/34



Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

PR-URL: https://github.com/nodejs/node/pull/18453


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yang Guo <yangguo@chromium.org>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>