Bug 32694: Fix value of 'Keep current' option in receiving

Bug 32694: Fix value of 'Keep current' option in receiving

This patch restores missing template toolkit markers around the variable

To test:
1 - Order an item in a basket
2 - Close the basket
3 - Attempt to receive the item, leaving budget as 'Keep current'
4 - 500 Error:
C4::Acquisition::ModReceiveOrder(): DBI Exception: DBD::mysql::st execute failed: Cannot add or update a child row: a foreign key constraint fails (koha_cclsny.aqorders, CONSTRAINT aqorders_budget_id_fk FOREIGN KEY (budget_id) REFERENCES aqbudgets (budget_id) ON DELETE CASCADE ON UPDATE CASCADE) at /usr/share/koha/intranet/cgi-bin/acqui/finishreceive.pl line 120
5 - Apply patch
6 - Receive order successfully!

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>