refactor(auth): better error message for method handler panic (#11482)

## Description

we panic when we attempt to register a msg that does not implement sdk.Msg. However, this is not immediately apparent in the panic error string. 

This PR updates the panic to be more specific as to why it panicked. 

Closes: n/a



---

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CHANGELOG.md

@@ -196,6 +196,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (x/auth) [\#10880](https://github.com/cosmos/cosmos-sdk/pull/10880) Added a new query to the tx query service that returns a block with transactions fully decoded.
 * (types) [\#11200](https://github.com/cosmos/cosmos-sdk/pull/11200) Added `Min()` and `Max()` operations on sdk.Coins.
 * (gov) [\#11287](https://github.com/cosmos/cosmos-sdk/pull/11287) Fix error message when no flags are provided while executing `submit-legacy-proposal` transaction.
+* (x/auth) [\#11482](https://github.com/cosmos/cosmos-sdk/pull/11482) Improve panic message when attempting to register a method handler for a message that does not implement sdk.Msg
 
 ### Bug Fixes
 

x/auth/middleware/msg_service_router.go

@@ -67,7 +67,7 @@ func (msr *MsgServiceRouter) RegisterService(sd *grpc.ServiceDesc, handler inter
 				// We panic here because there is no other alternative and the app cannot be initialized correctly
 				// this should only happen if there is a problem with code generation in which case the app won't
 				// work correctly anyway.
-				panic(fmt.Errorf("can't register request type %T for service method %s", i, fqMethod))
+				panic(fmt.Errorf("unable to register service method %s: %T does not implement sdk.Msg", fqMethod, i))
 			}
 
 			requestTypeName = sdk.MsgTypeURL(msg)