msggen: Allow non_camel_case for notification

In rust enum are expected to be CamelCase.
However, we are generating enum's using CAPITAL_SNAKE_CASE.

This generates a warning and breaks CI.

See `cln_rpc::notifications::ConnectAddressType::LOCAL_SOCKET`

cln-rpc/src/notifications.rs

@@ -1,3 +1,4 @@
+#![allow(non_camel_case_types)]
 // This file is autogenerated by `msggen`
 // Do not edit it manually, your changes will be overwritten
 

contrib/msggen/msggen/gen/rpc/notification.py

@@ -31,6 +31,7 @@ def generate_enum(self, service: Service):
         self.write("}\n")
 
     def generate(self, service: Service) -> None:
+        self.write("#![allow(non_camel_case_types)]\n")
         self.write("// This file is autogenerated by `msggen`\n")
         self.write("// Do not edit it manually, your changes will be overwritten\n\n\n")
         self.write("\n")