ggml: WebGPU disable SET_ROWS for now

[reeselevine]

test-thread-safety was recently updated to use SET_ROWS by default, but the WebGPU backend doesn't support it yet. I'm aiming to add support and open a PR in the next couple days, but in the meantime disabling SET_ROWS for the CI so the WebGPU tests pass.

[slaren]

Looks like it is still failing.

[reeselevine]

Sorry this CI failure for WebGPU on the Linux machine is turning out to be trickier than I expected. I haven't been able to reproduce it locally yet, only on the Github action runners using the simulated Vulkan LLVMpipe backend.

I'll keep working on it this week, to see if I can get a definitive answer into what's going on. In the meantime, would it make sense to just disable the WebGPU CI so it doesn't clutter up other PRs?

[reeselevine]

Looks like the CI is passing now, I was able to debug on the Github action runner using this: https://github.com/mxschmitt/action-tmate.

I believe the issue was due to not blocking on set_tensor calls. Not sure why it only causes issues on the LLVMpipe backend, but I suppose it's good that the CI caught the issue!

I also made another minor changes in this PR, to explicitly wait on Futures returned by WebGPU API callbacks before returning from graph_compute.

A few of the macOS CI tests are still queued, I'll wait for them to complete successfully before merging. Hopefully the WebGPU CI is more stable from here on!