Use Mambaforge for scheduled import testing (#1005)

Author: charlesbluca

.github/workflows/test-upstream.yml

@@ -138,9 +138,9 @@ jobs:
       - name: Set up Python
         uses: conda-incubator/[email protected]
         with:
+          miniforge-variant: Mambaforge
+          use-mamba: true
           python-version: "3.8"
-          mamba-version: "*"
-          channels: conda-forge,nodefaults
           channel-priority: strict
       - name: Optionally update upstream cargo dependencies
         if: env.which_upstream == 'DataFusion'