chore(tx): use buffer byte slice method directly (#24350)

Co-authored-by: Alex | Interchain Labs <alex@interchainlabs.io>

x/auth/client/tx.go

@@ -121,7 +121,7 @@ func ReadTxsFromInput(txCfg client.TxConfig, filenames ...string) (scanner *Batc
 				return nil, fmt.Errorf("couldn't read %s: %w", f, err)
 			}
 
-			if _, err := buf.WriteString(string(bytes)); err != nil {
+			if _, err := buf.Write(bytes); err != nil {
 				return nil, fmt.Errorf("couldn't write to merged file: %w", err)
 			}
 		}