Merge pull request #177 from KVSlab/dependabot/github_actions/actions…

…/cache-4

Bump actions/cache from 2 to 4

.github/workflows/build_docs.yml

@@ -64,7 +64,7 @@ jobs:
       - name: Set cache date
         run: echo "DATE=$(date +'%Y%m%d')" >> $GITHUB_ENV
 
-      - uses: actions/cache@v2
+      - uses: actions/cache@v4
         with:
           path: ${{ matrix.prefix }}
           key: ${{ matrix.label }}-conda-${{ hashFiles('environment.yml') }}-${{ env.DATE }}-${{ env.CACHE_NUMBER }}