test: update postmortem metadata test

This commit updates the following postmortem metadata constant:

- v8dbg_context_idx_closure
  - Renamed: v8dbg_context_idx_scope_info
  - V8 commit: https://github.com/v8/v8/commit/39496a95c53934ecb80d083003b4dd11056c9f20#diff-f3f182b0510ba2ee39ae87e421ff110b

Fixes: https://github.com/nodejs/node-v8/issues/59

PR-URL: https://github.com/nodejs/node/pull/21079


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yang Guo <yangguo@chromium.org>