fix: pass extra_pip_args to parse_requirements

[swarren12]

Bug fix for #2239.

The extra_pip_args variable was not being correctly passed to parse_requirements(), causing further calls to ignore anything that was set here.

This was a problem if, for example, the --trusted-host argument was needed to talk to the index set by experimental_index_url.

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[swarren12]

Seems like some of the builds are failing and I'm not sure if I'll have time to fix them on the fork.

Assuming people approve of this change, I'm happy for someone else to apply it outside of this PR.

[swarren12]

Fixed by #2258 so will close this one.