deps: update V8's postmortem script

This commit updates V8's postmortem metadata generation script
to support V8 7.8.

The following metadata has changed:

- v8dbg_class_JSDate__value__Object
  - The postmortem metadata generation script needed to be
    updated. No action should be required by postmortem tools.

- v8dbg_class_JSRegExp__source__Object
  - The postmortem metadata generation script needed to be
    updated. No action should be required by postmortem tools.

PR-URL: nodejs/node#29694
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>

common.gypi

@@ -39,7 +39,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.3',
+    'v8_embedder_string': '-node.4',
 
     ##### V8 defaults for Node.js #####