Fix bug Swimlanes headers partially sticky

ee/app/assets/javascripts/boards/components/epics_swimlanes.vue

@@ -178,7 +178,7 @@ export default {
     data_qa_selector="board_epics_swimlanes"
   >
     <swimlanes-loading-skeleton v-if="isLoading" />
-    <div v-else>
+    <div v-else class="board-swimlanes-content">
       <component
         :is="treeRootWrapper"
         v-bind="treeRootOptions"

ee/app/assets/stylesheets/page_bundles/boards.scss

@@ -100,6 +100,10 @@
 .board-swimlanes {
   overflow-x: auto;
 
+  .board-swimlanes-content {
+    height: fit-content;
+  }
+
   .board-add-new-list {
     height: calc(100% - 1rem);
   }

ee/changelogs/unreleased/bugfix-swimlanes-sticky-headers.yml

+---
+title: Fix Swimlanes sticky headers
+merge_request: 59944
+author:
+type: fixed