fix: Connector line position in tree view (#4062)

Author: cansuaa

src/tree-view/vertical-connector/styles.scss

@@ -7,23 +7,24 @@
 @use '../../internal/styles/tokens' as awsui;
 
 $item-toggle-column-width: 28px;
+$connector-line-width: awsui.$border-divider-list-width;
 
 .vertical-connector {
   background-color: awsui.$color-tree-view-connector-line;
-  inline-size: awsui.$border-divider-list-width;
+  inline-size: $connector-line-width;
 
   &.grid {
     grid-row: 2 / span 3;
     grid-column: 1;
     block-size: 100%;
     position: relative;
-    inset-inline-start: calc($item-toggle-column-width / 2);
+    inset-inline-start: calc(($item-toggle-column-width - $connector-line-width) / 2);
   }
 
   &.absolute {
     position: absolute;
     inset: 0;
     inset-block-end: awsui.$space-scaled-xs;
-    inset-inline-start: calc($item-toggle-column-width / 2);
+    inset-inline-start: calc(($item-toggle-column-width - $connector-line-width) / 2);
   }
 }