Upgrade gitlab-elasticsearch-indexer to version 2.16.0

What does this MR do and why?

Bumps up the version of the gitlab-elasticsearch-indexer to 2.16.0

The changes include:

• Drop deprecated -i flag from test target

Screenshots or screen recordings

N/A

How to set up and validate locally

N/A

MR acceptance checklist

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