Update installation instructions to use conda 23.10.0 or later

[stargaser]

Previously we modified our installation instructions to tell people how to install the libmamba library to make the conda installation go faster. As of conda version 23.10.0, libmamba is the default solver.

For the Astropy workshop installation, we are modifying the instructions to tell people to update their conda versions and check that they have version 23.10.0 or later. We should do the same for our instructions.