release-25.2: sql/importer: speed up TestImportCSVStmt

[yuzefovich]

Backport 1/1 commits from #160177 on behalf of @yuzefovich.

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Backport 1/1 commits from #159967.

/cc @cockroachdb/release

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In order to speed up the test we now use short intervals for the jobs subsystem via the testing knob.

Fixes: #160174
Release note: None

Release justification: test-only change.

[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 #160469 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The pull request is compliant because it only affects a test file, specifically 'pkg/sql/importer/import_stmt_test.go', which falls under the category of non-production code according to the policy. Furthermore, the PR body explicitly states that this is a 'test-only change', which accords with the exception for non-production and test-only changes in the backport policy.

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

[cockroach-teamcity]

This change is