ci: upload the dev preview artifact with forgejo/upload-artifact

actions/upload-artifact v4+ throws GHESNotSupportedError on this forge (run 169);
Forgejo's fork is the supported uploader.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.github/workflows/rat-dev-preview.yml

@@ -27,7 +27,8 @@ jobs:
       - name: Set background scene tier
         run: node scripts/preview-config.js low
       - name: Upload artifact
-        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        # Forgejo's fork: upstream upload-artifact v4+ refuses non-GitHub servers (GHESNotSupportedError).
+        uses: forgejo/upload-artifact@v4
         with:
           name: rat-dev-dist
           path: dist