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/+/2525147Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>