Fix pipeline failures of backfill_imported_issue_search_data_spec.rb in JH side

What does this MR do and why?

Related to issue #367436 (closed)

The test file spec/lib/gitlab/background_migration/backfill_imported_issue_search_data_spec.rb failed in JH side, The reason for the failure is that start_id is specified as 1 and end_id as 30 when the migration is initialized, so the test will fail once the issue ID exceeds 30.

let(:migration) do
  described_class.new(start_id: 1,
                      end_id: 30,
                      batch_table: :issues,
                      batch_column: :id,
                      sub_batch_size: 2,
                      pause_ms: 0,
                      connection: ApplicationRecord.connection)
end

/cc @prajnamas

Screenshots or screen recordings

How to set up and validate locally

Run bundle exec rspec ./spec/lib/gitlab/background_migration/backfill_imported_issue_search_data_spec.rb several times in the local development environment.

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