Update description of Visibility Scan API (#638)

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<!-- Describe what has changed in this PR -->
**What changed?**
Update description of Visibility Scan API

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**Why?**
Visibility Scan API has been marked as deprecated since Temporal
v1.27.0.
Temporal Server is changing to simply call the `List` API, so updating
the description so it is clear.

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**Breaking changes**


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**Server PR**
temporalio/temporal#8328

Author: rodrigozhou

temporal/api/workflowservice/v1/service.proto

@@ -458,7 +458,8 @@ service WorkflowService {
         };
     }
 
-    // ScanWorkflowExecutions is a visibility API to list large amount of workflow executions in a specific namespace without order.
+    // ScanWorkflowExecutions _was_ a visibility API to list large amount of workflow executions in a specific namespace without order.
+    // It has since been deprecated in favor of `ListWorkflowExecutions` and rewritten to use `ListWorkflowExecutions` internally.
     //
     // Deprecated: Replaced with `ListWorkflowExecutions`.
     // (-- api-linter: core::0127::http-annotation=disabled