Merge branch '281156-error-message-bar-overflows-old-boards-and-swimlanes-sidebar' into 'master'

Fix overlap of error message and sidebar on boards

See merge request gitlab-org/gitlab!70030

app/assets/stylesheets/page_bundles/boards.scss

@@ -430,6 +430,10 @@
   height: $input-height;
 }
 
+.issue-boards-content {
+  isolation: isolate;
+}
+
 .issue-boards-content.is-focused {
   position: fixed;
   width: 100%;