Summary:
PgIndexBackfillReadCommittedBlockIndislive.PhantomIdxEntry/1 is flaky and fails about 7/30 times sporadically.

This is due to a DML running right after Create Index, that may run into a "schema version mismatch".
Add a retry around the DML to make the test less flaky.
Jira: DB-17139

Test Plan:
Jenkins: test regex: PgIndexBackfillReadCommittedBlockIndislive.PhantomIdxEntry/1

yb_build.sh release  --cxx-test pg_index_backfill-test --gtest_filter PgIndexBackfillReadCommittedBlockIndislive.PhantomIdxEntry/1 --clang19 -n 30 --tp 3

Before this change, on master: 7 / 30 failures
Before https://github.com/yugabyte/yugabyte-db/commit/e01d18cce6760f7c9d4fd5b5336a9ceea4584ecd: 7 / 30 failures, so does not appear to be caused by that diff.
After this diff: 0 / 30

Reviewers: jason, hsunder

Reviewed By: jason, hsunder

Subscribers: ybase, yql

Differential Revision: https://phorge.dev.yugabyte.com/D44674