[Flax tests] Disable scheduled GPU tests

[patrickvonplaten]

What does this PR do?

The GPU tests are running forever at the moment and take up the whole gpu-test machine all the time. @patil-suraj we should probably sit together next week to investigate this a bit, make them much faster and then re-enable them.

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[HuggingFaceDocBuilder]

The documentation is not available anymore as the PR was closed or merged.

[LysandreJik]

LGTM. Happy to sit down with you and talk about it, I've observed similar slowdowns on per-model GPU flax tests.

[patrickvonplaten]

It's the compilation that takes for ever I think. I'll investigate a bit with @patil-suraj next week