chore(deps): update actions/cache action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -94,7 +94,7 @@ jobs:
       - run: yarn install --immutable
       - run: yarn build
       - name: Load RDF test suite cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: |
             .rdf-test-suite-cache