Fix provider type hint in SearchResponse

Author: mekarpeles

pyopds2/provider.py

@@ -69,7 +69,7 @@ def search(self, query: str, limit: int = 50, offset: int = 0) -> List[Publicati
     @dataclass
     class SearchResponse:
         """Response from a search query."""
-        provider: 'DataProvider'
+        provider: 'DataProvider | type[DataProvider]'
         query: str
         limit: int
         offset: int