MAINT: re-enable cache for ci (#270)

Author: mmcky

.github/workflows/ci.yml

@@ -41,13 +41,13 @@ jobs:
       - name: Display Pip Versions
         shell: bash -l {0}
         run: pip list
-      # - name: Download "build" folder (cache)
-      #   uses: dawidd6/action-download-artifact@v2
-      #   with:
-      #     workflow: cache.yml
-      #     branch: main
-      #     name: build-cache
-      #     path: _build
+      - name: Download "build" folder (cache)
+        uses: dawidd6/action-download-artifact@v2
+        with:
+          workflow: cache.yml
+          branch: main
+          name: build-cache
+          path: _build
       # Build Assets (Download Notebooks and PDF via LaTeX)
       - name: Build Download Notebooks (sphinx-tojupyter)
         shell: bash -l {0}