Bug 27142: Don't interpolate batch_type variable

Bug 27142: Don't interpolate batch_type variable

To test:
1 - Create a report like:
    SELECT * FROM borrowers LIMIT 50
2 - Run the report
3 - Attempt batch modification - it fails showing every row as an unfound cardnumber
4 - Apply patch
5 - Repeat
6 - Success!
7 - Edit report to:
    SELECT * FROM biblio LIMIT 50
8 - Repeat test
9 - Ensure batch modification and deletion work

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>