Explicit `pip` pin is dropped when `pip:` dependencies are present

[mdunphy]

Checklist

• I added a descriptive title
• I searched open reports and couldn't find a duplicate

What happened?

If an environment.yml contains both an explicit conda pin for pip and a pip: subsection, conda-lock replaces the explicit pin with pip * during solving.

Example:

name: test
channels:
  - conda-forge
dependencies:
  - python=3.12.1
  - pip=25.0.1
  - pip:
      - requests

When using conda-lock it loses the 25.0.1 pin:

INFO:conda_lock.conda_solver:linux-64 using specs ['python 3.12.1.*', 'pip *']

If I remove the pip section (last two lines), then it does not lose the pin:

INFO:conda_lock.conda_solver:linux-64 using specs ['python 3.12.1.*', 'pip 25.0.1.*']

This seems like a bug --- if the environment yaml explicitly specifies a conda-side pip constraint, that constraint should be preserved.

Additional Context

For what it's worth, Pixi does not have this issue, it respects the 25.0.1 pin with and without a pip section