cli: use the right context for logging on signal

[andreimatei]

We were using a long-gone context with a potentially finished span,
leading to log-after-finish crashes.

Fixes #26715

Release note: None

[cockroach-teamcity]

This change is 

[knz]

this may need backporting

[andreimatei]

the problem was introduced after 2.0

bors r+

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Review status: complete! 0 of 0 LGTMs obtained

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Comments from Reviewable

[knz]

the problem was introduced after 2.0

I see a call to stopper.Stop(ctx) in the log.FatalChan() case in start.go (v2.0). Shouldn't this use shutdownCtx instead?

[craig]

Build succeeded

• GitHub CI (Cockroach)

[andreimatei]

I see a call to stopper.Stop(ctx) in the log.FatalChan() case in start.go (v2.0). Shouldn't this use shutdownCtx instead?

Ah indeed, but that's a different enough bug. Will send a fix for that too.