Revert "Revert "Attempt to improve CI caching (#6534)" (#6543)"

This reverts commit 93b8813.

.github/workflows/ci-additional.yaml

@@ -69,6 +69,7 @@ jobs:
           else
             echo "CONDA_ENV_FILE=ci/requirements/${{ matrix.env }}.yml" >> $GITHUB_ENV
           fi
+
       - name: Cache conda
         uses: actions/cache@v3
         with:

.github/workflows/ci.yaml

@@ -82,12 +82,15 @@ jobs:
 
           echo "PYTHON_VERSION=${{ matrix.python-version }}" >> $GITHUB_ENV
 
+        # This and the next few are based on https://github.com/conda-incubator/setup-miniconda#caching-environments
       - name: Cache conda
+        id: cache-conda
         uses: actions/cache@v3
         with:
           path: ~/conda_pkgs_dir
           key: ${{ runner.os }}-conda-py${{ matrix.python-version }}-${{
             hashFiles('ci/requirements/**.yml') }}
+
       - uses: conda-incubator/setup-miniconda@v2
         with:
           channels: conda-forge
@@ -98,9 +101,18 @@ jobs:
           python-version: ${{ matrix.python-version }}
           use-only-tar-bz2: true
 
+      - name: Cache conda env
+        id: cache-env
+        uses: actions/cache@v3
+        with:
+          path: /usr/share/miniconda/envs/xarray-tests
+          key: ${{ runner.os }}-conda-py${{ matrix.python-version }}-${{
+            hashFiles('ci/requirements/**.yml') }}
+
       - name: Install conda dependencies
         run: |
           mamba env update -f $CONDA_ENV_FILE
+        if: steps.cache-env.outputs.cache-hit != 'true'
 
       # We only want to install this on one run, because otherwise we'll have
       # duplicate annotations.