Fix backend-plugin-api alpha api report

Signed-off-by: Philipp Hugenroth <philipph@spotify.com>

packages/backend-plugin-api/alpha-api-report.md

@@ -3,6 +3,12 @@
 > Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
 
 ```ts
+// @public (undocumented)
+export interface BackendFeature {
+  // (undocumented)
+  $$type: '@backstage/BackendFeature';
+}
+
 // @alpha (undocumented)
 export interface FeatureDiscoveryService {
   // (undocumented)
@@ -29,9 +35,5 @@ export type ServiceRef<
   $$type: '@backstage/ServiceRef';
 };
 
-// Warnings were encountered during analysis:
-//
-// src/alpha.d.ts:5:9 - (ae-forgotten-export) The symbol "BackendFeature" needs to be exported by the entry point alpha.d.ts
-
 // (No @packageDocumentation comment for this package)
 ```