pgsql: Fix background psql session cleanup in 051_effective_wal_level.p

Fix background psql session cleanup in 051_effective_wal_level.pl.

Commit 6aba42c660c added quit() calls for two background psql sessions
whose slot creation is canceled by pg_cancel_backend(). Both sessions
ran with the default ON_ERROR_STOP=1 and ended their script with \q,
so psql exited as soon as the cancellation error arrived. quit() then
wrote another \q to the already-closed pipe, making the test die with
"ack Broken pipe".

Run both sessions with on_error_stop => 0 and drop the trailing \q, so
that psql stays at the prompt after reporting the error and quit() can
shut it down cleanly.

Discussion: https://postgr.es/m/CAD21AoCZY1fKYgfkvHGWGiXpatUKd23FSLnDCL4m9bWFjdXNZw@mail.gmail.com
Backpatch-through: 19

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/5c808b8c5c395a7d7afea7efaaa3328b4bc4e004

Modified Files
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src/test/recovery/t/051_effective_wal_level.pl | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)