Bug 33046: Use process_tt in C4::Reports::Guided::EmailReport

Bug 33046: Use process_tt in C4::Reports::Guided::EmailReport

Bug 33030 implements a new helper subroutine to standardize processing of Template Toolkit syntax outside slips and notices. We should use this subroutine in EmailReport.

Test Plan:
1) Apply this patch
2) prove t/db_dependent/Reports/Guided.t

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>