Fix reindexing retry for the notes migration

ee/changelogs/unreleased/297646-fix-reindexing-retry.yml

+---
+title: Fix reindexing retry for the notes migration
+merge_request: 57248
+author:
+type: fixed

ee/elastic/migrate/20210302104500_migrate_notes_to_separate_index.rb

@@ -74,7 +74,7 @@ class MigrateNotesToSeparateIndex < Elastic::Migration
 
     set_migration_state(
       slice: slice,
-      task_id: task_id,
+      task_id: nil,
       retry_attempt: retry_attempt + 1,
       max_slices: max_slices
     )

ee/spec/elastic/migrate/20210201104800_migrate_notes_to_separate_index_spec.rb

@@ -147,6 +147,7 @@ RSpec.describe MigrateNotesToSeparateIndex do
             migration.set_migration_state(slice: 0, max_slices: 2, task_id: 'task_id')
 
             expect { migration.migrate }.to raise_error(/total is not equal/)
+            expect(migration.migration_state[:task_id]).to be_nil
           end
         end
 
@@ -159,6 +160,7 @@ RSpec.describe MigrateNotesToSeparateIndex do
             migration.set_migration_state(slice: 0, max_slices: 2, task_id: 'task_id')
 
             expect { migration.migrate }.to raise_error(/failed with/)
+            expect(migration.migration_state[:task_id]).to be_nil
           end
         end
       end