Fix support for pip>=22.1

[wizpig64]

Since #1607, which originally added 22.1 support, pip changed under the hood before release.

This PR fixes #1617, by moving an import inside the one function that needed it, which only ran under pip<22 anyway.

Contributor checklist

• Provided the tests for the changes.
• Assure PR title is short, clear, and good to be included in the user-oriented changelog

Maintainer checklist

• Assure one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[wizpig64]

The one failure aside from coverage is for python 3.11-dev. 3.11.0b1 was released recently, so someone ought to see if this is fixable too.

[atugushev]

Thanks!