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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -61,7 +61,7 @@ jobs:
           toolchain: stable
           targets: ${{ matrix.settings.target }}
       - name: Cache cargo
-        uses: actions/cache@v4
+        uses: actions/cache@v6
         with:
           path: |
             ~/.cargo/registry/index/