Merge pull request #961 from jupyterhub/dependabot/github_actions/act…

…ions/cache-4

build(deps): bump actions/cache from 3 to 4

.github/workflows/unit-test.yaml

@@ -70,7 +70,7 @@ jobs:
       #          completion. Make sure to update the key to bust the cache
       #          properly if you make a change that should influence it.
       - name: Load cached Python dependencies
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /srv/venv/
           key: >-