Update boards caret icon category and sizze

MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48068

app/assets/javascripts/boards/components/board_list_header.vue

@@ -190,7 +190,8 @@ export default {
         :title="chevronTooltip"
         :icon="chevronIcon"
         class="board-title-caret no-drag gl-cursor-pointer"
-        variant="link"
+        category="tertiary"
+        size="small"
         @click="toggleExpanded"
       />
       <!-- The following is only true in EE and if it is a milestone -->

app/assets/javascripts/boards/components/board_list_header_new.vue

@@ -198,7 +198,8 @@ export default {
         :title="chevronTooltip"
         :icon="chevronIcon"
         class="board-title-caret no-drag gl-cursor-pointer"
-        variant="link"
+        category="tertiary"
+        size="small"
         @click="toggleExpanded"
       />
       <!-- EE start -->

app/assets/stylesheets/page_bundles/boards.scss

@@ -92,7 +92,6 @@
   .board-title-caret {
     border-radius: $border-radius-default;
     line-height: $gl-spacing-scale-5;
-    height: $gl-spacing-scale-5;
 
     &.btn svg {
       top: 0;

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

@@ -131,7 +131,8 @@ export default {
           :title="chevronTooltip"
           :icon="chevronIcon"
           class="gl-mr-2 gl-cursor-pointer"
-          variant="link"
+          category="tertiary"
+          size="small"
           data-testid="epic-lane-chevron"
           @click="toggleCollapsed"
         />