Add pragma: full coverage to Process.is_alive (#2402)

uvicorn/supervisors/multiprocess.py

@@ -64,7 +64,7 @@ def target(self, sockets: list[socket] | None = None) -> Any:  # pragma: no cove
 
     def is_alive(self, timeout: float = 5) -> bool:
         if not self.process.is_alive():
-            return False
+            return False  # pragma: full coverage
 
         return self.ping(timeout)