Increase --finalize-streaming-on-background test coverage by enabling it
on the stress_js_bg_compile_wasm_code_gc variant.

Bug: chromium:1011762
Change-Id: I0df1ae9a1e73a9ce26f84c87136da1f89e9b18b3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2494929
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70733}