fix: Fix artifact action compatibility and add digest debugging

Resolve upload-artifact v4 GHES compatibility errors by downgrading to v3.
Switch to standard forgejo/download-artifact@v4 for pattern filtering support.
Update renovate configuration to prevent future incompatible upgrades.

Add diagnostic output to digest export step to troubleshoot zero-byte
artifact uploads preventing manifest creation. Include CI triggers for
Element workflow to test changes in pull requests.

.forgejo/workflows/element.yml

@@ -4,6 +4,14 @@ on:
   schedule:
     - cron: "0 0 * * *"
   workflow_dispatch:
+  pull_request:
+    paths:
+      - ".forgejo/workflows/element.yml"
+  push:
+    branches:
+      - main
+    paths:
+      - ".forgejo/workflows/element.yml"
 
 concurrency:
   group: "element-${{ github.ref }}"
@@ -101,7 +109,7 @@ jobs:
           cat ./element-web/webapp/config.json
 
       - name: 📤 Upload Artifact
-        uses: https://code.forgejo.org/actions/upload-artifact@v4
+        uses: https://code.forgejo.org/actions/upload-artifact@v3
         with:
           name: element-web
           path: ./element-web/webapp/