MDEV-36130: main.mysqldump fails in parallel mysql-import test

Skip printing the error if it is expected — that is, when mariadb-import
is aborting.

In a multithreading scenario, another thread may encounter an error
because the corresponding connection was killed. Do not print this error.

client/mysqlimport.cc

@@ -984,6 +984,8 @@ static void fatal_error(const char *format, ...)
 
 static void db_error(MYSQL *mysql)
 {
+  if (aborting)
+    return;
   const char *info= mysql_info(mysql);
   auto err= mysql_errno(mysql);
   auto err_text = mysql_error(mysql);