Make partitioned indexes eligible for reindexing

What does this MR do and why?

Makes partitioned indexes eligible for reindexing. Specifically, ci_builds indexes have been skipped from reindexing since the table was partitioned.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Try the following test to verify that this works for ci_builds:

    it 'includes ci_builds' do
      expect(described_class.reindexing_support.where("name = 'ci_builds_pkey'")).not_to be_empty
    end

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.