Describe the bug

Conda 23.7.3 was released and changed the way plugin commands were handled. This briefly broke mamba (mamba-org/mamba#2715), with a fix released in mamba-org/mamba#2732.

A consequence of this is that we should no longer call mamba mambabuild, but rather mamba build conda build, which forwards to the mamba solver if (as is the case in the CI environments) boa is installed.

We can't use mamba build due to mamba-org/mamba#2821