Ignores channel_sources

[bollwyvl]

Thanks for this tool!

problem

It looks like channel_sources is ignored.

background

I'm looking to update a chain of pre-releases, which specify:

channel_targets:
  - conda-forge/label/jupyterlab_alpha,conda-forge  

Which bulds (but hasn't been merged yet), and then:

channel_targets:
  - conda-forge notebook_alpha
channel_sources:
  - conda-forge/label/jupyterlab_alpha,conda-forge  

Which doesn't build locally:

 │ ╭─ Resolving environments
 │ │ 
 │ │ Resolving host environment:
 │ │   Platform: linux-64 [__unix=0=0, __linux=5.15.0=0, __glibc=2.34=0, __archspec=1=skylake]
 │ │   Channels: 
 │ │    - file:///home/conda/feedstock_root/build_artifacts/
 │ │    - conda-forge
 │ │   Specs:
 │ │    - hatch-jupyter-builder >=0.5
 │ │    - hatchling >=1.11
 │ │    - jupyterlab >=4.4.0a3,<4.5
 │ │    - pip
 │ │    - python 3.9.*
 │ │
 │ ╰─────────────────── (took 2 seconds)
 │
 ╰─────────────────── (took 2 seconds)
Error: 
  × Failed to resolve dependencies: Cannot solve the request because of: No candidates were found for jupyterlab >=4.4.0a3,<4.5.
  │ 
  ╰─▶ Cannot solve the request because of: No candidates were found for jupyterlab >=4.4.0a3,<4.5.

While I know that the jupyterlab one isn't up (still discussing how we might keep app working), I don't see how it could work, as there is no channel information present.

I haven't dug into this code vs conda-smithy, but it is handing over channel_urls, so suspect it might be here.

[minrk]

If channel_sources is showing up in the variant in .ci_support, I think that means there's an issue in rattler-build or the conda-smithy script templates (or both), not this package. This package is ~only used in rerendering, not during the build itself. I believe that's now tracked as prefix-dev/rattler-build#1416 does that seem right, @bollwyvl?