Conda-build 3 => update pinnings

[pkgw]

Checklist

• [x] Used a fork of the feedstock to propose changes
• [x] Bumped the build number (version is unchanged)
• [x] Re-rendered with the latest conda-smithy
• [x] 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.

[pkgw]

Stack overflow in rustc on macOS compiling a dependency ... some kind of bug in the latest release? Never seen anything like this before. Here's a similar problem in rustc on 1.27.1 on s390x.

[pkgw]

Seen in 1.28 too, sigh.

[pkgw]

OK well let's do the expedient thing and just anchor ourselves to building with 1.26.