[FIX] web: list: list_activity widget popover not visible

In edit mode, the list_activity widget popover is not fully visible
(most of it is cut). The reason is that at some point the rule
specifying that the containing list cell should have the property
'overflow: visible' became less important than another global
rule imposing the property 'overflow: hidden'.

The present commit makes sure that 'overflow: visible' is applied on all
list cells containing a list_activity widget.

Task ID: 2305805

closes odoo/odoo#56166

X-original-commit: 115fedf30da2ca016a2e435949a18561a389d37f
Signed-off-by: Lucas Perais (lpe) <lpe@odoo.com>

addons/mail/static/src/scss/mail_activity.scss

@@ -154,7 +154,7 @@
 .o_list_view {
     .o_list_table tbody > tr {
         > td.o_data_cell.o_list_activity_cell {
-            overflow: visible; // allow the activity dropdown to overflow
+            overflow: visible !important; // allow the activity dropdown to overflow
             .o_mail_activity {
                 display: flex;
                 max-width: 275px;