chore: update falcon/inspect.py per @CaselIT's suggestion

Co-authored-by: Federico Caselli <cfederico87@gmail.com>

falcon/inspect.py

@@ -90,7 +90,7 @@ def inspect_my_router(router):
     def wraps(fn):
         if router_class in _supported_routers:
             raise ValueError(
-                'Another function is already registered' ' for the router {}'.format(
+                'Another function is already registered for the router {}'.format(
                     router_class
                 )
             )