Bug fix for non-PSGallery repos adding script endpoint

[alerickson]

PR Summary

Bug fix for non-PSGallery v2 repositories adding "/items/psscript/" to the endpoint (an endpoint which only exists for the PSGallery). This was creating incorrect HTTP calls to non-PSGallery repositories and throwing terminating errors.

PR Context

Resolves #1485

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[adityapatwardhan]

Is it possible to add a test?