regress: fix test instability

Alvaro Herrera <alvherre@alvh.no-ip.org>

Commit: aa242501afb76d6806260bff3bc8494e0a7f2a69
Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2022-08-05T09:55:52Z
Releases: 15.0
regress: fix test instability

Having additional triggers in a test table made the ORDER BY clauses in
old queries underspecified.  Add another column there for stability.

Per sporadic buildfarm pink.

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