[FIX] mail: revert activity button spacing

In commit[1] we changed the spacing of the activity button to dissociate
it from buttons that are "message/communication" oriented.

This spacing was unwanted so we need to revert it back.

task-3730089

[1]: odoo/odoo@e0491c1a62

closes odoo/odoo#153100

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/core/web/chatter.xml

@@ -21,7 +21,7 @@
                     Log note
                 </button>
                 <div class="flex-grow-1 d-flex">
-                    <button t-if="props.hasActivities" class="o-mail-Chatter-activity btn btn-secondary ms-3 text-nowrap" t-att-class="{ 'my-2': !props.compactHeight }" data-hotkey="shift+a" t-on-click="scheduleActivity">
+                    <button t-if="props.hasActivities" class="o-mail-Chatter-activity btn btn-secondary text-nowrap" t-att-class="{ 'my-2': !props.compactHeight }" data-hotkey="shift+a" t-on-click="scheduleActivity">
                         <span>Activities</span>
                     </button>
                     <span class="o-mail-Chatter-topbarGrow flex-grow-1 pe-2"/>