release-24.2: kv: fix assertion in TestProxyTracing

[blathers-crl]

Backport 1/1 commits from #133609 on behalf of @nvanbenschoten.

/cc @cockroachdb/release

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This commit fixes the assertion in TestProxyTracing so that the test will fail if request proxying is not working as expected. The test was fooling itself, expecting QueryRowContext to return a nil Row if no matching trace event was found. This is not the case, as a nil Row is never returned. Instead, Row.Scan returns ErrNoRows if no matching row is found.

Also, the query wasn't even running because it was passing the last line of the query string in as a parameter, leading to the error: "pq: got 1 parameters but the statement requires 0".

I confirmed that before this change, the test passes even with request proxying disabled. After this change, the test fails.

Epic: None
Release note: None

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Release justification: testing only

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
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[cockroach-teamcity]

This change is