Update actions/cache action to v6 (#382)

Update actions/cache action to v6

Author: renovate[bot]

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
         uses: abatilo/actions-poetry@v4
 
       - name: Cache the virtualenv
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ~/.cache/pypoetry
           key: venv-${{ hashFiles('poetry.lock') }}