[FIX] web_kanban: column title overflow when folded

Commit 3b19fa426b fixed a bug where the column title of kanban group
was overflowing its area when too long. However, when the column is
folded, the title is now really small (width of the folded column)
and then stopped to add the "..." ellipsis.

The solution is to let the text overflow when the column is folded.

addons/web_kanban/static/src/less/kanban_view.less

@@ -424,6 +424,7 @@
                 top: 40px;
                 left: 15px;
                 position: absolute;
+                overflow: visible;
             }
             > .o_kanban_record, .o_kanban_quick_add, .o_kanban_config, .o_kanban_load_more {
                 display: none;