CI: Add conda cache

Author: zbrookle

.github/workflows/azure-pipelines.yml

@@ -22,6 +22,15 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v1
 
+    - name: Cache conda
+      uses: actions/cache@v1
+      env:
+        # Increase this value to reset cache if environment.yml has not changed
+        CACHE_NUMBER: 0
+      with:
+        path: ~/conda_pkgs_dir
+        key: ${{ runner.os }}-conda-${{ matrix.python }}-${{ env.CACHE_NUMBER }}-${{ hashFiles('environment.yml') }}
+
     - uses: conda-incubator/setup-miniconda@v2
       with:
         auto-update-conda: true