fix: update test expectations for validateOnly mode to include warnings field

Fixed failing CI test by updating test expectations to match the new response
structure that includes a details.warnings field in validateOnly mode.

Changes:
- Updated test mock to include warnings: [] in applyDiff response
- Updated test expectations to include details: { warnings: [] }

Related to issue #360 fix.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

tests/unit/mcp/handlers-workflow-diff.test.ts

@@ -188,6 +188,7 @@ describe('handlers-workflow-diff', () => {
         operationsApplied: 1,
         message: 'Validation successful',
         errors: [],
+        warnings: []
       });
 
       const result = await handleUpdatePartialWorkflow(diffRequest, mockRepository);
@@ -199,6 +200,9 @@ describe('handlers-workflow-diff', () => {
           valid: true,
           operationsToApply: 1,
         },
+        details: {
+          warnings: []
+        }
       });
 
       expect(mockApiClient.updateWorkflow).not.toHaveBeenCalled();