fix: restore proper gap on side-nav-items, adjust label gap (#10534)

Author: jouni

packages/aura/src/components/side-nav.css

@@ -4,14 +4,17 @@
   --vaadin-side-nav-label-font-weight: var(--aura-font-weight-medium);
   --vaadin-side-nav-item-font-weight: var(--aura-font-weight-medium);
   --vaadin-side-nav-item-border-width: 1px;
-  --vaadin-side-nav-item-gap: var(--vaadin-gap-xs);
   --vaadin-side-nav-items-gap: var(--vaadin-gap-xs);
 }
 
 vaadin-side-nav + vaadin-side-nav {
   margin-top: var(--vaadin-gap-l);
 }
 
+vaadin-side-nav::part(label) {
+  gap: var(--vaadin-gap-xs);
+}
+
 vaadin-side-nav-item::part(content) {
   --aura-surface-level: 4;
   --aura-surface-opacity: 0.6;