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

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -67,7 +67,7 @@ jobs:
           node-version: 24
 
       - name: Cache cargo registry
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: |
             ~/.cargo/registry
@@ -163,7 +163,7 @@ jobs:
           targets: ${{ matrix.settings.target }}
 
       - name: Cache cargo registry
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: |
             ~/.cargo/registry