Dependencies are lowercased before being pip-installed

Hi,

Dependencies are being lowercased before being pip-installed (well, written in the temporary requirements.txt file). This is an issue when trying to use eg GitLab deploy tokens to access a private library (it lowercases the token).

I might try a PR if I have the time/chance, otherwise I'm just leaving this here so that we can keep it in mind.

Trace where dependency names and credentials are written to the temporary requirements.txt before pip installation. Reproduce the issue with a mixed-case GitLab deploy token, then verify that the generated requirements and installation preserve its casing.

Written by the indexing model from the issue text.