pgsql: Provide a C-ctype variant expected file for test_regex_utf8

Provide a C-ctype variant expected file for test_regex_utf8

test_regex_utf8 decides whether to run by looking at the database
encoding alone, but two of its cases, [[:graph:]] and [[:print:]] over
E'xᔀሷ', depend on the ctype as well. In a database with encoding
UTF8 and locale C they match just the x, because isgraph() and isprint()
are false for anything outside ASCII, and the file fails.

No buildfarm animal builds such a cluster, which is why this went
unnoticed. A pending buildfarm client change will let an
animal be configured that way.

Fix by providing a second expected file holding the C-ctype answers, in
the manner of json_encoding.sql, which carries expected files for UTF8
and for SQL_ASCII. The .sql needs no change.

This applies to releases 15 and 16 only. A better solution is available
for release 17 and up.

Backpatch to v15, v16 only.

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/9ca3dfba7989ab62e172cfd611d8acdfd56606ac

Modified Files
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.../test_regex/expected/test_regex_utf8_2.out | 206 +++++++++++++++++++++
1 file changed, 206 insertions(+)