release-22.1: sql: do not close stmt buffer of internal executor in errCallback

[blathers-crl]

Backport 1/1 commits from #80070 on behalf of @yuzefovich.

/cc @cockroachdb/release

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Previously, we would close the stmt buffer of the internal executor in
errCallback, "just to be safe" since it was assumed that the buffer is
already closed when the callback is executed. The callback runs whenever
run() loop of connExecutor exits with an error.

However, it is possible for the following sequence of events to happen:

• The new goroutine is spun up for the internal executor before any
  commands are pushed into the stmt buffer.
• The context is canceled before the new goroutine blocks waiting for
  the command to execute, i.e. run() loop is exited before any commands
  are executed.
• The errCallback with the context cancellation error is evaluated.
  This closes the stmt buffer. The goroutine exits.
• The main goroutine tries to push some commands into the buffer only to
  find that it was already closed. An assertion error is returned, and
  a sentry event is created.

I think we should just not close the stmt buffer in the errCallback
since this was never necessary and can lead to the scenario described
above where no sentry event should be emitted.

Fixes: #79746.

Release note: None

---

Release justification: low risk bug fix.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[cucaroach]

[mgartner]

Do you want to backport this to 22.1.0 or can it wait until 22.1.1?

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @jordanlewis and @yuzefovich)

[yuzefovich]

It can definitely wait - the downside of not merging this are rare cases when the user will see an internal error (instead of user-friendly "query canceled" error) and we get a sentry report.