GN: Update trace tests build. Includes two small fixes: - add .gitignore for trace tests. - fix path for restricted traces, should fix bots. Bug: angleproject:4386 Change-Id: I51c657c4f2e772411e95faa76188d43c8b6981f7 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2057350 Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>