release-24.1: roachtest: deflake activerecord

[fqazi]

Backport 1/1 commits from #158200 on behalf of @fqazi.

---

Currently, the activerecord test can fail due to flakes inside client side encryption tests, which aren't linked to CRDB. To address this, this patch marks them as flaky.

Fixes: #157810

Release note: None

---

Release justification:

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

✅ PR #158227 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The pull request modifies a file 'pkg/cmd/roachtest/tests/activerecord_blocklist.go' that is categorized under non-production code as it pertains to roachtest, which is a development tool used for testing CockroachDB. Since the changes are confined to development tool infrastructure, the backport is exempt from the standard policy requirements regarding critical bugs and feature flags. Additionally, there is no requirement for a release justification text in cases where only non-production files are changed.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is