upgrade conda

[cat-bro]

The conda version was pinned to 4.12.0 during pawsey times. New versions of conda use mamba as the resolver so there would be no need to install mamba separately. This would save time running the galaxyproject.miniconda step of playbooks. There are currently maintenance issues with mamba - it will stop working every now and then and require a fresh install of ca-certificates... this just happened on dev.

Could just try using the latest version of conda which is far ahead of version 4. This probably needs to be done on dev first just to check that everything still works.