refactor(core): Improve test-webhooks (no-changelog) (#8069)

Remove duplication, improve readability, and expand tests for
`TestWebhooks.ts` - in anticipation for storing test webhooks in Redis.

---------

Co-authored-by: कारतोफ्फेलस्क्रिप्ट™ <aditya@netroy.in>

packages/workflow/src/Interfaces.ts

@@ -450,7 +450,6 @@ export interface IGetExecuteHookFunctions {
 		additionalData: IWorkflowExecuteAdditionalData,
 		mode: WorkflowExecuteMode,
 		activation: WorkflowActivateMode,
-		isTest?: boolean,
 		webhookData?: IWebhookData,
 	): IHookFunctions;
 }
@@ -1660,6 +1659,7 @@ export interface IWebhookData {
 	workflowId: string;
 	workflowExecuteAdditionalData: IWorkflowExecuteAdditionalData;
 	webhookId?: string;
+	isTest?: boolean;
 }
 
 export interface IWebhookDescription {