chore(deps): update actions/setup-node action to v6

Author: renovate[bot]

.github/workflows/test-credential-backends.yml

@@ -223,7 +223,7 @@ jobs:
               exit 1
             fi
           '
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: 24
       - name: Test Node.js spawn + stdin with secret-tool
@@ -295,7 +295,7 @@ jobs:
           else
             echo "Verify deleted: OK"
           fi
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: 24
       - name: Test Node.js execFile with security command