Fix handling of search term when performing searches from the sidebar

Signed-off-by: Johan Hammar <johan.hammar@gmail.com>

.changeset/neat-cooks-sell.md

@@ -0,0 +1,5 @@
+---
+'@backstage/core-components': patch
+---
+
+Fix search in Firefox. When the search was performed by pressing enter, the query parameter was first set but then reverted back.

packages/core-components/src/layout/Sidebar/Items.tsx

@@ -311,6 +311,7 @@ export function SidebarSearchField(props: SidebarSearchFieldProps) {
   const handleEnter: KeyboardEventHandler = ev => {
     if (ev.key === 'Enter') {
       search();
+      ev.preventDefault();
     }
   };