sql: deflake TestReadCommittedStmtRetry

[nvanbenschoten]

Fixes #123661.

This commit deflakes TestReadCommittedStmtRetry by not enabling the hook to block writes in the Read Committed transaction until after the first write. This avoids flakiness if the first write is ever retried due to slowness in the cluster, lease instability, or some other reason.

Release note: None

[cockroach-teamcity]

This change is 

[rafiss]

nice, thank you for the fix!

[nvanbenschoten]

TFTR!

bors r+

[craig]

Build succeeded:

• linux_amd64_build
• windows_build
• examples_orms
• linux_amd64_fips_build
• linux_arm64_build
• lint
• macos_arm64_build
• check_generated_code
• local_roachtest_fips
• macos_amd64_build
• acceptance
• local_roachtest
• docker_image_amd64
• unit_tests

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from 421a23b to blathers/backport-release-23.2-123957: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 23.2.x failed. See errors above.

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