Gitlab::Elastic::Indexer::Error: Cannot load such file -- elasticsearch/git (LoadError)

https://sentry.gitlap.com/gitlab/gitlabcom/issues/13629/

Gitlab::Elastic::Indexer::Error: /opt/gitlab/embedded/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- elasticsearch/git (LoadError)
	from /opt/gitlab/embedded/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from /opt/gitlab/embedded/service/gitlab-rails/bin/elastic_repo_indexer:6:in `<main>'

  lib/gitlab/elastic/indexer.rb:36:in `run'
    raise Error, output unless status.zero?
  lib/gitlab/metrics/instrumentation.rb:155:in `block in run'
    trans.method_call_for(#{label.to_sym.inspect}).measure { super }
  lib/gitlab/metrics/method_call.rb:23:in `measure'
    retval = yield
  lib/gitlab/metrics/instrumentation.rb:155:in `run'
    trans.method_call_for(#{label.to_sym.inspect}).measure { super }
  app/workers/elastic_commit_indexer_worker.rb:16:in `perform'
    indexer.run(
...
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