Add pytest to CI - #6

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, conda-incubator/setup-miniconda@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

warning libmamba Security Warning: This transaction includes executing package scripts (pre/post-link/unlink) if present. These scripts can contain arbitrary code. Please ensure you trust the package sources.

The 'defaults' channel might have been added implicitly. If this is intentional, add 'defaults' to the 'channels' list. Otherwise, consider setting 'conda-remove-defaults' to 'true'.

warning libmamba Security Warning: This transaction includes executing package scripts (pre/post-link/unlink) if present. These scripts can contain arbitrary code. Please ensure you trust the package sources.