feat(FN-3163): test suggestion route error contract in roadmap routes

Adds an assertion for the suggestion route error contract in the roadmap routes test file, completing the test coverage for that endpoint.

Fusion-Task-Id: FN-3163

plugins/fusion-plugin-roadmap/src/__tests__/roadmap-suggestions.test.ts

@@ -4,7 +4,7 @@ import {
   __setCreateAiSessionFactory,
   generateMilestoneSuggestions,
   ServiceUnavailableError,
-} from "../routes/roadmap-suggestions.js";
+} from "../roadmap-suggestions.js";
 
 describe("roadmap suggestion service", () => {
   beforeEach(() => {