Update actions/cache action to v6 (#874)

Update actions/cache action to v6

Author: renovate[bot]

.github/workflows/build.yml

@@ -24,7 +24,7 @@ jobs:
         run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Setup Composer cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('composer.lock') }}

.github/workflows/docs.yml

@@ -36,7 +36,7 @@ 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') }}