Bug 25236: Fix semantic heading for opac-full-serial-issues.tt

Prior to this patch, the opac-full-serial-issues side navigation box contained
semantically incorrect headings.

Test plan
1/ Search for a serial with many linked issues
2/ Navigate to the detailed view of that serial
3/ Click on the 'More details' link after all the listed issues
4/ Inspect the 'Refine your search' elements on the left side of the screen.
   Note that the headings are H1 (Koha page title) > H4 (Refine your search)
3/ Apply this patch
4/ Reload the page
5/ Re-inspect the 'Refine your search' elements and note the heading
   semantics are now H1 (Title of page) > H2 (Refine your search)
6/ Note the appearance of the box is improved and consistent with elsewhere
7/ Signoff

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 0550e0b7f7)

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

koha-tmpl/opac-tmpl/bootstrap/en/modules/opac-full-serial-issues.tt

@@ -25,17 +25,19 @@
                 <div class="span2">
                     <div id="searchfacetscontainer">
                         <div id="search-facets">
-                            <h4>Refine your search</h4>
                             <form action="/cgi-bin/koha/opac-serial-issues.pl" id="filterform">
-                                <fieldset>
+                            <h2><a href="#" class="menu-collapse-toggle">Refine your search</a></h2>
+                            <ul class="menu-collapse">
+                                <li>
                                     <label for="libraryfilter">Library: </label>
                                     <select id="libraryfilter" name="libraryfilter" style="width:10em;"></select>
                                     <label for="subscriptionidfilter">Subscription: </label>
                                     <select id="subscriptionidfilter" name="subscriptionfilter" style="width:10em;" disabled="disabled"></select>
-                                </fieldset>
-                                <fieldset class="action">
+                                </li>
+                                <li class="action">
                                     <input type="reset" id="reset" class="btn" value="Clear" />
-                                </fieldset>
+                                </li>
+                            </ul>
                             </form>
                         </div> <!-- / #search-facets -->
                     </div> <!-- / #searchfacetscontainer -->