Gold Trace Tests: Fix JSON output with empty test set. Previously we would leave an empty test suite name with no tests run. According to the JSON test results spec this is likely a malformed output and we should instead include just an empty "tests" key. Bad: "tests": { "angle_restricted_trace_gold_tests": {} } Good: "tests": {} Bug: angleproject:5299 Change-Id: I459da593df150d804130f9c63e05d031e77a16a3 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2525147 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>