CI install-conda.sh is raising EnvironmentLocationNotFound

[leehart]

E.g. when removing pinned env files and upgrading malariagen_data package (as usual) #157 https://github.com/malariagen/mgenv/actions/runs/11666157311/job/32480463432?pr=157

Downloading and Extracting Packages: ...working... done
Preparing transaction: ...working... done
Verifying transaction: ...working... done
Executing transaction: ...working... done
Python 3.12.2
conda 24.9.2
# packages in environment at /home/runner/work/mgenv/mgenv/deps/conda:
#
# Name                    Version                   Build  Channel
conda-libmamba-solver     24.9.0             pyhd8ed1ab_0    conda-forge

EnvironmentLocationNotFound: Not a conda environment: /home/runner/work/mgenv/mgenv/deps/conda/envs/mgenv-68c5276

Error: Process completed with exit code 1.

This is blocking other PRs, e.g. #153

[leehart]

It looks like the install-conda.sh is currently failing because the line:

conda env remove -v --name=$CONDANAME

...assumes that $CONDANAME exists. I guess because it would usually have been created on a previous run. However, when it does not exist (for whatever reason) any attempt to remove a non-existent env will raise an error, such as:

EnvironmentLocationNotFound: Not a conda environment: /home/runner/work/mgenv/mgenv/deps/conda/envs/mgenv-b0a4b9e

...where $CONDANAME has been set to mgenv-b0a4b9e.