BUG: ordering: values in migrator not working when using additional_zip_keys for that key

[h-vetinari]

The current state of scipy (conda-forge/scipy-feedstock@07e1f9f) is broken with the latest smithy and needs manual fixes to the rerender.

The issue is that we have a local channel config (necessary for new enough flang), which conflicts with what the python 3.13 migrator wants to do.

The proper solution to this is IMO to override the migrator locally so that it knows how to order the various channel_sources, which worked in similar scenarios already, e.g. for the numpy 2 migration (conda-forge/scipy-feedstock@93e11f6). I did the same for the python 3.13 migration (conda-forge/scipy-feedstock@af35e4e), however, smithy misrenders the channels on windows to be

--- a/.ci_support/win_64_numpy2.1python3.13.____cp313.yaml
+++ b/.ci_support/win_64_numpy2.1python3.13.____cp313.yaml
@@ -3,7 +3,7 @@ c_compiler:
 c_stdlib:
 - vs
 channel_sources:
-- conda-forge/label/python_rc,conda-forge/label/llvm_rc,conda-forge
+- conda-forge/label/python_rc,conda-forge
 channel_targets:
 - conda-forge main
 cxx_compiler:

despite the ordering. AFAICT, the config that triggers the difference in behaviour is

    additional_zip_keys:
        - channel_sources

I understand that it's a bit of a rare combination (migration with extra channel against feedstock that needs another extra channel, and it's an additional_zip_keys), but I had a moment and thought I'd raise it for completeness.