[IMP] mail: change timestamp color in the systray

The timestamp color should be gray instead of primary green even when the thread is unread or needs action.

Task id: 2383054

closes odoo/odoo#71034

Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/mail/static/src/components/notification_list/notification_list_item.scss

@@ -143,7 +143,7 @@ $o-mail-notification-list-item-muted-hover-background-color:
 @mixin o-mail-notification-list-item-date-style() {
     @include o-mail-notification-list-item-bold-style();
     font-size: x-small;
-    color: $o-brand-primary;
+    color: gray('500');
 }
 
 @mixin o-mail-notification-list-item-image-style {

addons/mail/static/src/components/thread_preview/thread_preview.scss

@@ -94,10 +94,6 @@
 
 .o_ThreadPreview_date {
     @include o-mail-notification-list-item-date-style();
-
-    &.o-muted {
-        color: gray('500');
-    }
 }
 
 .o_ThreadPreview_image {