fix(simapp): concurrent map writes when calling GetSigners (backport #21073) (#21130)

Co-authored-by: Facundo Medica <14063057+facundomedica@users.noreply.github.com>
Co-authored-by: Julien Robert <julien@rbrt.fr>
Co-authored-by: Facundo <facundomedica@gmail.com>

simapp/app.go

@@ -209,6 +209,10 @@ func NewSimApp(
 	legacyAmino := codec.NewLegacyAmino()
 	txConfig := tx.NewTxConfig(appCodec, tx.DefaultSignModes)
 
+	if err := txConfig.SigningContext().Validate(); err != nil {
+		panic(err)
+	}
+
 	std.RegisterLegacyAminoCodec(legacyAmino)
 	std.RegisterInterfaces(interfaceRegistry)