Fix incorrect range in pg_regress comment.
A comment in pg_regress incorrectly stated that alternative
output files could be named test_{i}.out with 0 < i <= 9.
However, the valid range is actually 0 <= i <= 9.
(The user-facing docs have this right already.)
Author: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
Discussion: https://postgr.es/m/
6e6c4dea-07a1-4a83-9bb7-
77b9b3324c37@tantorlabs.com