pgsql: Try a few different locale name spellings in nls.sql.

Try a few different locale name spellings in nls.sql.

While CI testing in advance of commit 8c498479d suggested that all
Unix-ish platforms would accept 'es_ES.UTF-8', the buildfarm has
a different opinion. Let's dynamically select something that works,
if possible.

Discussion: https://postgr.es/m/E1vUpNU-000kcQ-1D@gemulon.postgresql.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5b275a6e154833803d3beb49da0879d2fe8b1d6c

Modified Files
--------------
src/test/regress/expected/nls.out | 21 +++++++++++++++++----
src/test/regress/expected/nls_1.out | 21 +++++++++++++++++----
src/test/regress/sql/nls.sql | 21 +++++++++++++++++----
3 files changed, 51 insertions(+), 12 deletions(-)