This fixes a handle leaking out of
V8HeapExplorer::ExtractPropertyReferences when enabling
v8_dict_mode_prototypes, which breaks the
test-heap-profiler/NoHandleLeaks cctest.

Bug: v8:11388
Change-Id: I911f60e3701277540ae5a63fa59f3ac2f52879ef
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2748580Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Frank Emrich <emrich@google.com>
Cr-Commit-Position: refs/heads/master@{#73319}