Trigger "Report Size Deltas" workflow run when workflow file is modified

This provides a "smoke test" to validate proposed changes to the workflow.

Author: per1234

.github/workflows/report-size-deltas.yml

@@ -1,6 +1,9 @@
 name: Report Size Deltas
 
 on:
+  push:
+    paths:
+      - ".github/workflows/report-size-deltas.ya?ml"
   schedule:
     - cron: '*/5 * * * *'
   # See: https://docs.github.com/en/free-pro-team@latest/actions/reference/events-that-trigger-workflows#workflow_dispatch