Fix signals problem on sentry.io (#1732)

When using the newest version of the Python SDK on the sentry backend we get the following error:

name = "partial(<function " + receiver.func.__name__ + ">)"  # type: ignore
AttributeError: __name__

This change gets the __name__ attribute in a very defensive way, to not raise any errors what so ever.

sentry_sdk/integrations/django/signals_handlers.py

@@ -25,7 +25,8 @@ def _get_receiver_name(receiver):
     elif hasattr(
         receiver, "func"
     ):  # certain functions (like partials) dont have a name
-        name = "partial(<function " + receiver.func.__name__ + ">)"  # type: ignore
+        if hasattr(receiver, "func") and hasattr(receiver.func, "__name__"):  # type: ignore
+            name = "partial(<function " + receiver.func.__name__ + ">)"  # type: ignore
 
     if (
         name == ""