split variants in WebGPU's cts.html for less timouts

[sagudev]

We need more fine grained solution either via splitting test or adding timeout only to specific tests (or both).

OLD:
I though I catch all [FAIL/PASS, TIMEOUT, NOTRUN], but apparently not. To prevent them from happening it would be bast to have variants for flaky tests.

See: gpuweb/cts#3233

[sagudev]

I am currently waiting for gpuweb/cts#3246 to land.

[sagudev]

Currently this was resolved (somehow) in #31695, by just disabling such flaky test. But now in #31772 I observed some real timeouts that would be solved by more fine chunking.

Solution as noted in #31772 (comment), is to chunk only problematic test per max time.

[sagudev]

Times from Chrome are completely different (servo/FF: 18s vs chrome 20ms), so we would need to generate our own time data for it to work (can we share data with firefox).

Moving to timeout long produced this results (from current main): https://github.com/sagudev/servo/actions/runs/8456974386/job/23169503338.

In the future we can move all test that need more time in separate html file so meta long will effect only them.