chore(gov): improve proposal conversion error message (backport #15979)…

… (#15980)

Co-authored-by: Julien Robert <julien@rbrt.fr>
Co-authored-by: marbar3778 <marbar3778@yahoo.com>

CHANGELOG.md

@@ -37,6 +37,10 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ## [Unreleased]
 
+### Improvements
+
+* (gov) [#15979](https://github.com/cosmos/cosmos-sdk/pull/15979) Improve gov error message when failing to convert v1 proposal to v1beta1.
+
 ## [v0.47.2](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.47.2) - 2023-04-27
 
 ### Improvements

x/gov/migrations/v3/convert.go

@@ -49,7 +49,7 @@ func ConvertToLegacyProposal(proposal v1.Proposal) (v1beta1.Proposal, error) {
 		return v1beta1.Proposal{}, err
 	}
 	if len(msgs) != 1 {
-		return v1beta1.Proposal{}, sdkerrors.ErrInvalidType.Wrap("can't convert a gov/v1 Proposal to gov/v1beta1 Proposal when amount of proposal messages is more than one")
+		return v1beta1.Proposal{}, sdkerrors.ErrInvalidType.Wrap("can't convert a gov/v1 Proposal to gov/v1beta1 Proposal when amount of proposal messages not exactly one")
 	}
 	if legacyMsg, ok := msgs[0].(*v1.MsgExecLegacyContent); ok {
 		// check that the content struct can be unmarshalled