Our test SQL connection doesn't always read its own writes:
it can use different connections for different queries.
So
```
INSERT INTO foo;
feed(CREATE CHANGEFEED FOR foo)
```
is a race condition. This just doesn't matter for most tests
because if the insert happens after the initial scan, it creates
the same payload. But tests with initial_scan='only' won't see it
at all.

Fixes cockroachdb#92211

Release note: None