Build Electron before packaging

Author: MarkJamesHoward

.github/workflows/electron-build.yml

@@ -31,6 +31,10 @@ jobs:
         working-directory: electron
         run: npm ci
 
+      - name: Build app
+        working-directory: electron
+        run: npm run build
+
       - name: Build installers
         working-directory: electron
         run: npm run dist