CI: Use miniforge because conda no longer included on GitHub runner images - #1263

The run was canceled by @slivingston.

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

`auto-activate-base` is deprecated. Please use `auto-activate`. If your installer does not use the `base` environment as the default environment, also add `activate-environment: base`.

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.

warning libmamba 'repo.anaconda.com', a commercial channel hosted by Anaconda.com, is used. warning libmamba Please make sure you understand Anaconda Terms of Services. warning libmamba See: https://legal.anaconda.com/policies/en/

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.

`auto-activate-base` is deprecated. Please use `auto-activate`. If your installer does not use the `base` environment as the default environment, also add `activate-environment: base`.