fix: recommend facetName should be string

Author: kai687

specs/recommend/common/schemas/TrendingFacetsQuery.yml

@@ -8,6 +8,7 @@ trendingFacets:
   type: object
   properties:
     facetName:
+      type: string
       description: Facet attribute for which to retrieve trending facet values.
     model:
       $ref: '#/trendingFacetsModel'