v5.7.1

MixedModels v5.7.1

NEWS file.
Diff since v5.7.0

NB: Closed issues and pull requests are sorted temporally and so may
include backports to other versions or work in the development branch for
an upcoming breaking release. Please see the NEWS file
for changes sorted by release.

Merged pull requests:

• Bump codecov/codecov-action from 6 to 7 (#900) (@dependabot[bot])
• Bump actions/checkout from 6 to 7 (#901) (@dependabot[bot])
• update the "other packages" documentation (#902) (@palday)
• update to new MixedModelsDatasets and tweak some tolerances (#904) (@palday)