correct Announcement.__str__() to present hex (#14740)

A hash is quite unlikely to be valid UTF-8 data and even if it does decode it seems unlikely to be a useful representation.

chia/types/announcement.py

@@ -21,4 +21,4 @@ class Announcement:
         return std_hash(bytes(self.origin_info + message))
 
     def __str__(self):
-        return self.name().decode("utf-8")
+        return self.name().hex()