add return type to the 'run' function

Author: jyecusch

nitric/application.py

@@ -88,7 +88,7 @@ def _create_tracer(cls, local: bool = True, sampler: int = 100) -> TracerProvide
         return provider
 
     @classmethod
-    def run(cls):
+    def run(cls) -> None:
         """
         Start the nitric application.