use mamba-org/setup-micromamba in CI tests (#1136)

Author: oxidase

.github/workflows/main.yml

@@ -26,13 +26,12 @@ jobs:
     - uses: actions/checkout@v2
 
     - name: Setup conda
-      uses: conda-incubator/setup-miniconda@v2
+      uses: mamba-org/setup-micromamba@v1
       with:
         environment-file: environment-dev.yml
-        activate-environment: ipyleaflet-dev
-        mamba-version: "*"
-        python-version: ${{ matrix.python-version }}
-        channels: conda-forge
+        condarc: |
+          dependencies:
+            - python==${{ matrix.python-version }}
 
     - name: Install ipyleaflet
       run: pip install . --no-deps