fix flax-latest-hf-bert-mnli-func-v2-8 timeout (#749)
fix flax-latest-hf-bert-mnli-func-v2-8 timeout (#749)

This test usually takes about an hour to run, extend the time limit.
TESTED=flax-latest-hf-bert-mnli-func-v2-8-1vm-85b5b
GoogleCloudPlatform/ml-testing-accelerators,GoogleCloudPlatform/ml-testing-accelerators