[FIX] project: IE11 issue with kanban overflow

In 6fd7fc9 the issue was solved in some instance, but there was still an
issue with the combination of IE11 / Odoo community / Overflowing content.

fixes #9696

related to opw-653477

addons/project/static/src/less/project_dashboard.less

@@ -6,9 +6,9 @@
     }
 
     .o_project_kanban_main {
-        .o-flex(1, 0, 0);
+        .o-flex(0, 0, auto);
         padding: @odoo-horizontal-padding;
-        max-width: 70%; // for IE11 overflow issue
+        width: 70%; // for IE11 overflow issue
 
         // give space for manage section at the bottom
         margin-bottom: @odoo-horizontal-padding/2 + 19px;