Update dependencies

[tjtg]

This PR updates the list of dependencies in the recipe to match the conda-forge environment file introduced in metoppv/improver#1589.

Other changes, such as running the unit test suite against the built conda package, will need to wait for a tagged release which includes changes from that PR, then create another PR on this repository.

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-linter]

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.

[lucyleeow]

LGTM. Checked that it matches envs/conda-forge.yml in improver. Just one question, do we need pip here?

[tjtg]

Just one question, do we need pip here?

Pip is listed under the host requirements section. That makes it available when the package is getting built, so it can be used for the build script python -m pip install . -vv on line 15.
This usage of pip is recommended in the conda-forge docs and seems to be common in other feedstock repos such as iris and xarray.