ci: install Electron before the cross-version wire job

The suite imports host/renderer wire modules that load Electron. Without
the package binary, Electron's installer downloads at import time and has
no retry, so a single GitHub CDN flake fails the job before any test runs.

.github/workflows/pr.yml

@@ -305,6 +305,12 @@ jobs:
         with:
           native-runtime: node
 
+      # Same as the sharded `test` job: importing host/renderer wire modules
+      # loads Electron, and Electron's own installer has no retry. The dedicated
+      # script retries GitHub CDN flakes instead of failing the suite at import.
+      - name: Install Electron package binary for tests
+        run: node config/scripts/install-electron-package-binary.mjs
+
       # A path filter that matches nothing exits 1 ("No test files found"), so this
       # lane cannot report success while running zero tests.
       - name: Old/new client and server terminal journey