ci(jest): run jest balance every two weeks (#40728)

.github/workflows/jest-balance.yml

@@ -1,5 +1,8 @@
 name: jest balancer
-on: [workflow_dispatch]
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 1,15 * *'
 jobs:
   jest-balance:
     # Buckle up, this may take a while