Build sim container once an hour

.github/workflows/sim_tests.yaml

@@ -1,14 +1,14 @@
 name: simulator
 on:
-  push:
-  pull_request:
+  schedule:
+  - cron: '0 * * * *'
 
 jobs:
   docker_build:
     name: build container
     runs-on: ubuntu-16.04
     timeout-minutes: 50
-    if: github.repository == 'commaai/openpilot'
+    if: github.event_name == 'schedule' && github.repository == 'commaai/openpilot'
     steps:
     - uses: actions/checkout@v2
       with: