Bug 34494: Table tmp_holdsqueue fails to be created for MySQL 8

Bug 34494: Table tmp_holdsqueue fails to be created for MySQL 8

It appears that MySQL 8 rejects creating any table where the primary key is nullable. The table tmp_holdsqueue has a nullable pk ( itemnumber ) but there is no reason for this column to be nullable ( generating a holds queue entry with no itemnumber is not possible ) so it make sense to just remove the nullability for MySQL compatiability.

Test Plan:
1) Using MySQL 8.0, attempt to create a database from kohastructure.sql
   If you use ktd, you can try:  DB_IMAGE=mysql:8.0 ktd up
2) Note the failure to create the table
3) Apply this patch
4) Repeat step 1
5) The table is created!

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>