bug: CI tests are not working due to incompatible python and mamba version

[fgypas]

Describe the bug

In the CI we specify Python 3.7.4 and mamba 0.16. See here: https://github.com/zavolanlab/zarp/blob/dev/.github/workflows/ci.yml#L27-L28

As mentioned in #108 for unknown reasons it defaults to Python 3.10. But Python 3.10 is incompatible with mamba 0.16 so the tests CI fails at the beginning.

Expected behavior
It should work for all python versions.

Additional context
One solution would be to not specify exact mamba version. So switch to mamba-version: "*" from mamba-version: "0.16.0".

Also this link has some related info: conda-incubator/setup-miniconda#274

[uniqueg]

I think not pinning a version for Mamba is a very good idea! But we should still upgrade Python as described in #109.