Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/modules/search/migration_templates/d6_search_settings.yml

@@ -1,5 +1,5 @@
 id: d6_search_settings
-label: Drupal 6 search configuration
+label: Search configuration
 migration_tags:
   - Drupal 6
 source:

core/modules/search/migration_templates/d7_search_settings.yml

@@ -1,5 +1,5 @@
 id: d7_search_settings
-label: Drupal 7 search configuration
+label: Search configuration
 migration_tags:
   - Drupal 7
 source:

core/modules/search/migration_templates/search_page.yml

@@ -1,7 +1,8 @@
-id: d6_search_page
-label: Drupal 6 search page configuration
+id: search_page
+label: Search page configuration
 migration_tags:
   - Drupal 6
+  - Drupal 7
 source:
   plugin: variable
   variables:
@@ -20,6 +21,6 @@ process:
   path: 'constants/path'
   plugin: 'constants/plugin'
   'configuration/rankings':
-    plugin: d6_search_configuration_rankings
+    plugin: search_configuration_rankings
 destination:
   plugin: entity:search_page