feat(pip-compile): Provide credentials for registries in all input files

[mbudnek]

Changes

Pip-compile can compile multiple input files into one lock file. Renovate calls the manager's updateArtifacts function once for each input file, but currently it only looks for private package registries in the input file currently being processed. This changes it to look for them in all of the input files.

Context

#28958

Documentation (please check one with an [x])

• [ ] I have updated the documentation, or
• [x] No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• [ ] Code inspection only, or
• [ ] Newly added/modified unit tests, or
• [ ] No unit tests but ran on a real repository, or
• [x] Both unit tests + ran on a real repository