ENH: lint incorrect distro names in os_version

[h-vetinari]

This is for linting wrong distro values used in os_version (which becomes more important after conda-forge/conda-forge-pinning-feedstock#6626, as it might lead to zipping problems and thus rerender errors).

With this PR, a conda-forge.yml of

os_version:
  linux_64: wrong

would lead to

pydantic_core._pydantic_core.ValidationError: 1 validation error for ConfigModel
os_version.linux_64
  Input should be 'cos7', 'ubi8', 'alma8' or 'alma9' [type=literal_error, input_value='wrong', input_type=str]
    For further information visit https://errors.pydantic.dev/2.10/v/literal_error

We'll certainly want to polish this further (e.g. into a concrete hint/lint), hence this is a draft. It's also a draft because by themselves, the changes in dc74f55 do not work. It needs #1920 (or something similar) to actually work, see #2152. Currently it includes that PR, which should be merged first.