pgsql: Avoid using ambiguous word "positive" in error message.

Avoid using ambiguous word "positive" in error message.

There are two identical error messages about valid value of modulus for
hash partition, in PostgreSQL source code. Commit 0e1275fb07 improved
only one of them so that ambiguous word "positive" was avoided there,
and forgot to improve the other. This commit improves the other.
Which would reduce translator burden.

Back-pach to v11 where the error message exists.

Author: Kyotaro Horiguchi
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/20210819.170315.1413060634876301811.horikyota.ntt@gmail.com

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7d9026cbfd340a4de6c96ff7c728e53c3791e1cc

Modified Files
--------------
src/backend/parser/parse_utilcmd.c         | 2 +-
src/test/regress/expected/alter_table.out  | 2 +-
src/test/regress/expected/create_table.out | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)