search: fix alpha plugin id

Co-authored-by: Camila Belo <camilaibs@gmail.com>
Co-authored-by: Philipp Hugenroth <philipph@spotify.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/three-moles-mix.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-search': patch
+---
+
+Fixed incorrect plugin ID in `/alpha` export.

plugins/search/src/alpha.tsx

@@ -243,7 +243,7 @@ export const SearchNavItem = createNavItemExtension({
 
 /** @alpha */
 export default createPlugin({
-  id: 'plugin.search',
+  id: 'search',
   extensions: [SearchApi, SearchPage, SearchNavItem],
   routes: {
     root: convertLegacyRouteRef(rootRouteRef),