Fix conda setup

sagemath/sage#36468

Author: grst

.github/workflows/conda.yml

@@ -26,8 +26,9 @@ jobs:
         uses: conda-incubator/setup-miniconda@v2
         with:
           auto-update-conda: true
-          mamba-version: "*"
-          channels: conda-forge,bioconda,defaults
+          miniforge-version: latest
+          use-mamba: true
+          channels: conda-forge,bioconda
           channel-priority: true
           python-version: 3.8