CI jobs should fail immediately (or retry) if package install fails

[bryevdv]

Seen this a few times, where the prepare environment step will fail (e.g. due to transient conda bad gateway) but then proceed to try to run the tests, e.g. https://github.com/bokeh/bokeh/actions/runs/8989165483/job/24691806627?pr=13874

Ideally the GH action for the conda env could retry some number of times. But failing that, it would still be better if the job ends immediately if an env cannot be successfully created.