Bug 26314: (follow-up) Make title search explicit

Bug 26314: (follow-up) Make title search explicit

This patch updates the get_volumes_query search returned when
UseControlNumber is disabled such that it matches the query produced by
XSLT sheets by replacing the ->title accessor with the more specific
->subfield('245', "a") accessor to just take subfield `a` into account.

Signed-off-by: Michaela Sieber <michaela.sieber@kit.edu>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>