Try out per-repo filtering (#1181)

diff --git a/.github/workflows/update_submodules.yml b/.github/workflows/update_submodules.yml
index de529dc..2c55dd8 100644
--- a/.github/workflows/update_submodules.yml
+++ b/.github/workflows/update_submodules.yml
@@ -18,11 +18,13 @@
 
 on:
   schedule:
-     # Every weekday at 14:00 UTC (06:00 PST/07:00 PDT)
-     - cron: '0 14 * * 1-5'
+     # Every five minutes
+     - cron: '*/5 * * * *'
 
 jobs:
   update:
+    # Don't run this in everyone's forks.
+    if: github.repository == 'gmngeoffrey/iree'
     runs-on: ubuntu-18.04
     steps:
       - name: Checking out repository