Bump actions/upload-artifact to v6 for Node.js 24 support

GitHub Actions warns that Node.js 20 will be removed from runners on
2026-09-16, with the forced switch to Node.js 24 starting 2026-06-02.
upload-artifact@v6 runs on Node.js 24 by default.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: seto77

.github/workflows/release.yml

@@ -205,7 +205,8 @@ jobs:
 
       - name: Upload workflow artifacts
         if: steps.version.outputs.needed == 'true'
-        uses: actions/upload-artifact@v4
+        # 260425Cl Node.js 20 廃止対応 (v6 で Node.js 24 がデフォルト)
+        uses: actions/upload-artifact@v6
         with:
           name: ReciPro-installer-v.${{ steps.version.outputs.version }}
           path: ${{ steps.build_installer.outputs.msi_path }}