Bug 25151: Fixing semantic headings in opac-basket.tt

Bug 25151: Fixing semantic headings in opac-basket.tt

Test plan:
1) Apply the patch
2) Add items to your cart/folder/basket
3) Open up the basket and check that the main heading is now an h1
4) Check that the page looks fine

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit f002bd17105bab2d16aee8db8ed4f6d688192fc3)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>