Do not use `--extra-index-url` in testing wheels (#100183)
Should prevent regressions like the ones reported in https://github.com/pytorch/pytorch/issues/100104 from sneaking undetected.
Same for `install_triton_wheel.sh` - always use packages from https://download.pytorch.org/whl/
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### <samp>🤖 Generated by Copilot at deda821</samp>
> _`pip install` changed_
> _Only use PyTorch nightly_
> _Snowflake packages_
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100183
Approved by: https://github.com/kit1980, https://github.com/pmeier
