[Backport 2.x] Update bwc test to update index setting (#2236)

[VijayanB]

Description

Backport https://github.com/opensearch-project/k-NN/commit/cbf90f5a456108fa49ffb85020f3edf7e307420e to 2.x

Related Issues

Check List

• [ ] New functionality includes testing.
• [ ] New functionality has been documented.
• [ ] API changes companion pull request created.
• [x] Commits are signed per the DCO using --signoff.
• [ ] Public documentation issue/PR created.

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