Run pip check during tests

[MridulS]

This ensures that there isn't a drift between pypi and conda metadata.
While adding sans-fitter to conda-forge I ran into a pip check failure as the sasmodels pypi package depends on tccbox and columnize but those packages aren't present in the conda recipe. The pip check will catch these failures earlier. Keeping it draft first to test out the CI.

Checklist

• 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 @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[conda-forge-admin]

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/meta.yaml) and found it was in an excellent condition.

[MridulS]

It fails as expected.