Python3: Update generate_test_spec_json.py Bug: angleproject:5707 Change-Id: Ifa84ecfc4f718f2798b232da30613b8af4940a7a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3475171 Auto-Submit: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>