Pin libmambapy <2

[jaimergp]

Description

libmambapy 2.0rc is out so let's prevent breakage for the upcoming 24.7 release. I'll issue repodata patches too:

• https://github.com/conda-forge/conda-forge-repodata-patches-feedstock/pull/800
• https://github.com/AnacondaRecipes/repodata-hotfixes/pull/234

Checklist - did you ...

• [x] Add a file to the news directory (using the template) for the next release's release notes?
• [ ] Add / update necessary tests?
• [ ] Add / update outdated documentation?