fix: pin miniforge to working version 25.9.1

Basically, this is only until this problem's fix (which already seems to exist), is either patched and/or released in `conda-libmamba-solver`, probably via `conda` itself:
conda/conda-libmamba-solver#798

Author: dlaehnemann

action.yml

@@ -78,7 +78,7 @@ runs:
       with:
         channels: conda-forge,bioconda
         channel-priority: strict
-        miniforge-version: latest
+        miniforge-version: 25.9.1 # TODO: set back to "latest" once this issue in the conda-libmamba-solver is patched and/or released: https://github.com/conda/conda-libmamba-solver/issues/798
         environment-file: .snakemake.environment.yaml
         activate-environment: snakemake