This fixes a -Wshadow warning for NO_FLAG. The other option is to
make it an enum class, which makes test-conversions.cc a bit verbose.

Bug: v8:12244,v8:12245
Change-Id: I3ea429eb45e31b25d4c6658ceb86c33ba280ae51
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3274015Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77860}