infra: Fix exclusion spec JSON. The extra comma caused the CQ to fail reading the file. Bug: angleproject:5114 Change-Id: I5d36f1ae7c4dc5ebcb5599d5cd37471ee4085990 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2876985 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>