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

Author: renovate[bot]

.github/workflows/release.yml

@@ -21,7 +21,7 @@ jobs:
       # these if statements ensure that a publication only occurs when
       # a new release is created:
       if: ${{ steps.release.outputs.release_created }}
-    - uses: actions/setup-node@v4
+    - uses: actions/setup-node@v6
       with:
         node-version: 20
         cache: yarn

.github/workflows/test.yml

@@ -69,7 +69,7 @@ jobs:
       - name: Prepare NodeBB package.json
         run: cp install/package.json package.json
         working-directory: nodebb
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: ${{ matrix.node }}
       - name: Install plugin dependencies