Run integration test workflow periodically to catch external breakage

The project infrastructure may be broken by changes to the external dependencies (e.g., GitHub Actions runner changes,
runner machine OS/environment updates, action releases, tool releases).

If this breakage is not caught and fixed quickly by the maintainer, it may cause confusion to the contributors whose
contributions trigger a spurious workflow run failure.

Monitoring for breakage can be done by periodically triggering a workflow run.

Author: per1234

.github/workflows/test-integration.yml

@@ -23,6 +23,10 @@ on:
       - "action.yml"
       - "compilesketches/**"
 
+  schedule:
+    # Run periodically to catch breakage caused by external changes.
+    - cron: "0 12 * * THU"
+
 env:
   SKETCHES_REPORTS_PATH: sketches-reports
   TESTDATA_PLATFORMS_PATH: .github/workflows/testdata/platforms