release-25.1: sql: always wait for all goroutines in fingerprintSpan

[yuzefovich]

Backport 1/1 commits from #148700 on behalf of @yuzefovich.

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This commit fixes an oversight from 1cf6236. In particular, in that change we ensured that we never leak the worker goroutines in fingerprintSpan by cancelling the context in the coordinator and checking for that in the workers. However, it was possible for the coordinator to exit before the workers which can lead to undefined behavior down the line (in a test failure we just saw usage of the trace span after finish). This commit fixes the oversight by always blocking the coordinator until all its workers exit.

Fixes: #148602.

Release note: None

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Release justification: low-risk bug fix.

[blathers-crl]

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[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is