This is a very small change which must go in before
https://chromium-review.googlesource.com/c/chromium/src/+/1731108
is able to land.

Certain WPT tests for synthetic modules were spawning DCHECK crashes by JSObject::SetNormalizedProperty.

Export names were previously failing:
DCHECK(name->IsUniqueName());

This small change corrects the issue and allows Module::GetModuleNamespace to run correctly.
This change aligns synthetic module behavior for export string storage with JS modules, as well as the spec.

chromium: 967018
Change-Id: I151e7150290bd72d4e4753c8c5be243eafae915f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1761583Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63264}