ci: schedule a daily build

Schedule a daily build, so that we can quickly spot regressions in the
application due to changes in Zephyr.

Signed-off-by: Gerard Marull-Paretas <[email protected]>

Author: gmarull

.github/workflows/build.yml

@@ -1,6 +1,10 @@
 name: Build
 
-on: [push, pull_request]
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: "0 0 * * *"
 
 jobs:
   build: