Add additional trigger events to CI workflows

Schedule event allows periodic checks for breakage caused by external changes. This is important both because it brings
these issues to the developer's attention, and also so that breakage to the CI can be fixed before it causes contributors
to have a bad experience from irrelevant failures of check on their PRs.

The workflow_dispatch and repository_dispatch events allow manual triggering of the workflow. These can be useful when
doing development and maintenance on the CI system, and do no harm when they are not needed, so it makes sense to add
them.

Author: per1234

.github/workflows/compile-examples.yml

@@ -11,6 +11,11 @@ on:
       - ".github/workflows/compile-examples.yml"
       - "examples/**"
       - "src/**"
+  schedule:
+    # Run every Tuesday at 8 AM UTC to catch breakage caused by changes to external resources (libraries, platforms).
+    - cron: "0 8 * * TUE"
+  workflow_dispatch:
+  repository_dispatch:
 
 jobs:
   build:

.github/workflows/spell-check.yml

@@ -6,6 +6,8 @@ on:
   schedule:
     # run every Tuesday at 3 AM UTC
     - cron: "0 3 * * 2"
+  workflow_dispatch:
+  repository_dispatch:
 
 jobs:
   spellcheck: