Put parens around extra-mark-short-names as well

This just looks more uniform.

aleksis/apps/alsijil/templates/alsijil/partials/register_abbreviations.html

@@ -37,7 +37,7 @@
   <ul class="collection">
     {% for extra_mark in extra_marks %}
       <li class="collection-item">
-        <strong>{{ extra_mark.short_name }}</strong> {{ extra_mark.name }}
+        <strong>({{ extra_mark.short_name }})</strong> {{ extra_mark.name }}
       </li>
     {% endfor %}
   </ul>

aleksis/apps/alsijil/templates/alsijil/partials/register_members_table.html

@@ -23,7 +23,7 @@
     {% endfor %}
     <th>{% trans '(b)' %}</th>
     {% for extra_mark in extra_marks %}
-      <th>{{ extra_mark.short_name }}</th>
+      <th>({{ extra_mark.short_name }})</th>
     {% endfor %}
   </tr>
   </thead>