Bug 32550: (bug 28445 follow-up) Fix 'Clear on loan' link on item batch mod

Bug 32550: (bug 28445 follow-up) Fix 'Clear on loan' link on item batch mod

The 'Clear on loan' link displayed at the top of the batch item
modification tool has been broken by bug 28445.

data-is-onloan attribute is supposed to be 1 or 0, but we passed the
checkout (Koha::Checkout=HASH)

Test plan:
1. Enter a checked-out barcode in the 'Batch item modification' page
2. Click 'Continue'
3. Notice a table is loaded displaying the on-loan item with a ticked checkbox 4. Click the 'Clear on loan' link above the table
5. Notice the on-loan item is no longer selected

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>