gha: Attempt (cached) mamba

.github/workflows/impl.yml

@@ -27,12 +27,24 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v3
 
+      - name: Cache conda
+        uses: actions/cache@v2
+        env:
+          # Increase this value to reset cache if etc/example-environment.yml has not changed
+          CACHE_NUMBER: 0
+        with:
+          path: ~/conda_pkgs_dir
+          key:
+            ${{ runner.os }}-conda-${{ env.CACHE_NUMBER }}-${{hashFiles( format('{0}/{1}/{2}', 'implementations/', inputs.implementation, '/environment.yml') ) }}
+
       - name: Setup miniconda
         uses: conda-incubator/setup-miniconda@v1
         with:
           auto-update-conda: true
-          channels: conda-forge,ome
+          channels: conda-forge,defaults
+          channel-priority: true
           environment-file: implementations/${{ inputs.implementation }}/environment.yml
+          mamba-version: "*"
           python-version: ${{ inputs.python-version }}
         env:
           ACTIONS_ALLOW_UNSECURE_COMMANDS: true