CI: bump GitHub Actions to Node 24 runtimes

Node 20 is deprecated on GitHub-hosted runners. Bump the affected
actions to their current Node 24 majors (upload-artifact v7,
download-artifact v8, setup-node v5).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: stangri

.github/workflows/openwrt-release.yml

@@ -233,7 +233,7 @@ jobs:
           done
 
       - name: 📦 Upload artifact for ${{ matrix.target }}
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: ${{ env.PKG_NAME }}-${{ matrix.target }}-${{ matrix.version }}
           path: |
@@ -264,7 +264,7 @@ jobs:
           echo "version=$COMBINED_VERSION" >> "$GITHUB_OUTPUT"
 
       - name: ⬇️ Download all build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           path: ./release-assets