Bug 36630: Change Post to GET to fix CSRF error on item search batch operations buttons

Bug 36630: Change Post to GET to fix CSRF error on item search batch operations buttons

This patch changes the form that submits to batchMod.pl from the Item search results page. The form method does not need to be a POST.

    To recreate:

    1. Do an item search
    2. On the results page 'click Select visible rows'
    3. Click 'Batch operations' and select 'Batch item modification'
    4. See Programming error - op 'show' must start with 'cud-' for POST http://localhost:8081/intranet/tools/batchMod.pl (referer: http://localhost:8081/cgi-bin/koha/catalogue/itemsearch.pl)
    5. Click 'Batch operations' and select 'Batch item deletion'
    6. See the same error

    To test:
    1. Apply patch and repeat steps to recreate the issue
    2. See that the batchMod.pl page loads with no error.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>