Add pip cache to the Anaconda tests

.github/workflows/test.yml

@@ -178,6 +178,19 @@ jobs:
           path: ~/conda_pkgs_dir
           key: conda-${{ runner.os }}-${{ matrix.python }}-${{ hashFiles('requirements*.txt') }}
 
+      - name: Get pip cache dir
+        id: pip-cache
+        run: |
+          echo "::set-output name=dir::$(pip cache dir)"
+
+      - name: pip cache
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.pip-cache.outputs.dir }}
+          key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
+
       - name: Setup Miniconda
         uses: conda-incubator/setup-miniconda@v2
         with: