Exec checks if tx is closed

https://github.com/jackc/pgx/discussions/1350

tx.go

@@ -201,6 +201,10 @@ func (tx *dbTx) Rollback(ctx context.Context) error {
 
 // Exec delegates to the underlying *Conn
 func (tx *dbTx) Exec(ctx context.Context, sql string, arguments ...any) (commandTag pgconn.CommandTag, err error) {
+	if tx.closed {
+		return pgconn.CommandTag{}, ErrTxClosed
+	}
+
 	return tx.conn.Exec(ctx, sql, arguments...)
 }