Duo Workflow: Update sequence diagram with auth

Why is this change being made?

This update clarifies the authentication mechanisms in use for each request.

Related discussion: gitlab-org&16549 (comment 2321842620)

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Commits

• Duo Workflow: Update sequence diagram with auth

• Follow up to conversation here: gitlab-org&16549 (comment 2321842620)

---

content/handbook/engineering/architecture/design-documents/duo_workflow/_index.md

@@ -155,8 +155,6 @@ sequenceDiagram
 
 #### With Remote (CI pipeline) execution
 
-Yellow boxes indicate auth mechanism for each request.
-
 ```mermaid
 sequenceDiagram
     autonumber