Fix `conda_build.config.subdir` deprecation (pt. 2)

[jakirkham]

Fixes https://github.com/conda-forge/conda-forge-ci-setup-feedstock/issues/317

Checklist

• [x] Used a personal fork of the feedstock to propose changes
• [ ] Bumped the build number (if the version is unchanged)
• [ ] Reset the build number to 0 (if the version changed)
• [ ] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

[conda-forge-webservices[bot]]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[jakirkham]

Skipped bumping the version as the last PR ( https://github.com/conda-forge/conda-forge-ci-setup-feedstock/pull/318 ) already bumped it and CI cannot upload without this fix anyways ( https://github.com/conda-forge/conda-forge-ci-setup-feedstock/issues/317#issuecomment-2109138263 )

[github-actions[bot]]

Hi! This is the friendly conda-forge automerge bot!

I considered the following status checks when analyzing this PR:

• linter: passed
• azure: passed

Thus the PR was passing and merged! Have a great day!