[FIX] mail: allow scroll in activity menu

Before this commit, it was not possible to scroll
inside long activity menu.

Dropdown already manage scroll, so the content should not put
overflow management, to the risk of introducing scrollbar twice
or making content non-scrollable.

Task-3249174

closes odoo/odoo#116815

Signed-off-by: Louis Wicket (wil) <wil@odoo.com>

addons/mail/static/src/web/activity/activity_menu.xml

@@ -12,7 +12,7 @@
                 <div t-if="store.activityGroups.length === 0" class="o-mail-ActivityMenu-empty align-items-center text-muted p-2 opacity-50 d-flex justify-content-center">
                     <span>Congratulations, you're done with your activities.</span>
                 </div>
-                <div class="d-flex flex-column overflow-hidden cursor-pointer" name="activityGroups">
+                <div class="d-flex flex-column cursor-pointer" name="activityGroups">
                     <t t-foreach="store.activityGroups" t-as="group" t-key="group.id" name="activityGroupLoop">
                         <div class="o-mail-ActivityGroup d-flex p-2 border-bottom" t-att-data-model_name="group.model" t-on-click="() => this.openActivityGroup(group)">
                             <img alt="Activity" t-att-src="group.icon"/>