Document 3-level restriction for workflow_run (#22508)

* Document 3-level restriction for workflow_run

* Update content/actions/learn-github-actions/events-that-trigger-workflows.md

* Update content/actions/learn-github-actions/events-that-trigger-workflows.md

Co-authored-by: Lucas Costi <lucascosti@users.noreply.github.com>

Co-authored-by: Lucas Costi <lucascosti@users.noreply.github.com>

content/actions/learn-github-actions/events-that-trigger-workflows.md

@@ -808,7 +808,15 @@ on:
 
 {% data reusables.webhooks.workflow_run_desc %}
 
-{% data reusables.github-actions.branch-requirement %}
+{% note %}
+
+**Notes:** 
+
+* This event will only trigger a workflow run if the workflow file is on the default branch.
+
+* You can't use `workflow_run` to chain together more than three levels of workflows. For example, if you attempt to trigger five workflows (named `B` to `F`) to run sequentially after an initial workflow `A` has run (that is: `A` → `B` → `C` → `D` → `E` → `F`), workflows `E` and `F` will not be run.
+
+{% endnote %}
 
 | Webhook event payload | Activity types | `GITHUB_SHA` | `GITHUB_REF` |
 | --------------------- | -------------- | ------------ | -------------|