fix(driver-utils): add missing return type to policies getter

Add explicit return type to satisfy @typescript-eslint/explicit-function-return-type rule.

Co-Authored-By: anthony-murphy <anthony.murphy@microsoft.com>
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: 3 people

packages/loader/driver-utils/src/test/prefetchDocumentStorageService.spec.ts

@@ -57,7 +57,7 @@ class MockStorageService implements Partial<IDocumentStorageService> {
 		};
 	}
 
-	public get policies() {
+	public get policies(): undefined {
 		return undefined;
 	}
 }