conda env export is outdated

[andrewgait]

https://github.com/UoMResearchIT/programming_with_python/blob/d0bf10d1adf272e13a351a15d63b04adf3b12645/episodes/04-software_package_management.md?plain=1#L396

According to the conda env export docs, we should now be using conda export instead of conda env export.

The sequence of commands is then (for example)

conda export --from-history --file myenvfile.yaml
conda env create --name mynewenv --file myenvfile.yaml

Using conda list in the suggested way in the notes does also still work. Using conda env export to create a txt or yaml file gives me errors of the form

CondaValueError: invalid package specification: name: myenv

when trying to (re)create an environment using conda env create.