Fix mamba setup

Author: jrbourbeau

.github/workflows/tests.yml

@@ -26,7 +26,6 @@ jobs:
       - name: Setup Conda Environment
         uses: conda-incubator/setup-miniconda@v3
         with:
-          miniforge-variant: Mambaforge
           miniforge-version: latest
           use-mamba: true
           channel-priority: strict