CI: fix Conda builds

Author: rouault

.github/workflows/conda.yml

@@ -34,8 +34,10 @@ jobs:
 
     - uses: conda-incubator/setup-miniconda@v3
       with:
-        miniforge-variant: Mambaforge
         miniforge-version: latest
+        use-mamba: true
+        channels: conda-forge
+        auto-update-conda: true
 
     - name: Setup
       shell: bash -l {0}