UpdateWorkflowVersionStep returns client input without valid field, violating non-nullable GraphQL schema

https://sonarly.com/issue/14051?type=bug

The `updateWorkflowVersionStep` mutation returns the raw client-provided step JSON as the GraphQL response without ensuring all non-nullable fields (specifically `valid`) are populated, causing a GraphQL serialization error.

Fix: After computing `updatedStep` from either the type-change or settings-only path, the code now creates a `normalizedUpdatedStep` that ensures the `valid` field is always populated. If the client-provided step includes `valid`, that value is used; otherwise, it falls back to `existingStep.valid` (the step stored in the database, which always has this field).

The `normalizedUpdatedStep` is used both for persisting to the database (in `updatedSteps`) and as the GraphQL return value, ensuring consistency and preventing the `Cannot return null for non-nullable field WorkflowAction.valid` error.

This follows the exact same normalization pattern previously applied for the `position` field (commit d2746d2778), addressing the same class of bug where the `updateWorkflowVersionStep` mutation returns raw client input without ensuring all non-nullable GraphQL DTO fields are populated.

packages/twenty-server/src/modules/workflow/workflow-builder/workflow-version-step/workflow-version-step-update.workspace-service.ts

@@ -73,9 +73,16 @@ export class WorkflowVersionStepUpdateWorkspaceService {
           additionalCreatedSteps: undefined,
         };
 
+    const normalizedUpdatedStep = {
+      ...updatedStep,
+      valid: isDefined(updatedStep.valid)
+        ? updatedStep.valid
+        : existingStep.valid,
+    };
+
     const updatedSteps = workflowVersion.steps.map((existingStep) => {
       if (existingStep.id === step.id) {
-        return updatedStep;
+        return normalizedUpdatedStep;
       } else {
         return existingStep;
       }
@@ -93,7 +100,7 @@ export class WorkflowVersionStepUpdateWorkspaceService {
       },
     );
 
-    return updatedStep;
+    return normalizedUpdatedStep;
   }
 
   private async updateWorkflowVersionStepType({