[MOD] update actions/cache to v4 [skip ci]

Author: alexnuttinck

.github/workflows/tests.yml

@@ -42,7 +42,7 @@ jobs:
           pip install --upgrade pip
           pip install -r requirements-${{ matrix.plone-version }}.txt
       - name: Cache eggs
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         env:
           cache-name: cache-eggs
         with: