ci: run builds periodically

There is not much activity happening in neard, thus workflows triggered
on changes might never run.  In the same time distros actually change.
Run at least once per week, to be sure it still builds even without
development activity.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e8e708c..677c415 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,7 +7,13 @@
 # Loosely based on https://github.com/linux-test-project/ltp
 #
 name: "Builds"
-on: [push, pull_request, workflow_dispatch]
+on:
+  pull_request:
+  push:
+  schedule:
+    # Run at 1:01 AM, every Tuesday
+    - cron: '1 1 * * 2'
+  workflow_dispatch:
 
 jobs:
   job: