Fix swagger UI for split specs (#2002)

Fixes #1909 

This PR uses the already resolved spec when swagger UI requests it.

Author: RobbeSneyders

connexion/middleware/swagger_ui.py

@@ -63,7 +63,7 @@ def _base_path_for_prefix(self, request: StarletteRequest) -> str:
             "route_root_path", request.scope.get("root_path", "")
         ).rstrip("/")
 
-    def _spec_for_prefix(self, request):
+    def _spec_for_prefix(self, request) -> dict:
         """
         returns a spec with a modified basePath / servers block
         which corresponds to the incoming request path.

connexion/spec.py

@@ -204,7 +204,7 @@ def enforce_string_keys(obj):
         return OpenAPISpecification(spec, base_uri=base_uri)
 
     def clone(self):
-        return type(self)(copy.deepcopy(self._raw_spec))
+        return type(self)(copy.deepcopy(self._spec))
 
     @classmethod
     def load(cls, spec, *, arguments=None):