Restrict further the use of anaconda default channels

We have switched our conda environment to use miniforge instead of miniconda, but tests showed that some operations could still trigger the use of package channels other than conda-forge.

This update to the latest version of miniforge, combined with an update to the condarc file that is shipped with conda-analytics aims to make it even more difficult to pull in packages from these repositories whose licence may be incomaptible with our operations.

Bug: T383284