Bug 35422: Fix translation of suggestions title tag

Bug 35422: Fix translation of suggestions title tag

This patch corrects a missed instance of a string in the title tag which
should have been wrapped in the translation function [% t() %]

To test, apply the patch and go to Suggestions.

- Click "New purchase suggestion"
- The title of the page should be correct: "Add suggestion"
- Confirm that translation is improved:
  - Update and reinstall active translations (for instance fr-FR):
    perl misc/translator/translate update fr-FR
  - Check the corresponding po file, in this case fr-FR-messages.po
  - There should be an entry for the string "Add suggestion"

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit d485ff32b0949f1e39bb5325a4dbb49db89ec582)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>