pg_regress: for --no-locale, use LOCALE='C'.

Instead of specifying LC_COLLATE='C' and LC_CTYPE='C', specify
LOCALE='C' which will also affect ICU. This makes pg_regress
consistent with recent changes to initdb in commit a14e75eb0b.

Fixes buildfarm failure.

Discussion: https://postgr.es/m/2458565.1686953169@sss.pgh.pa.us

src/test/regress/pg_regress.c

@@ -1972,10 +1972,10 @@ create_database(const char *dbname)
 	 */
 	if (encoding)
 		psql_add_command(buf, "CREATE DATABASE \"%s\" TEMPLATE=template0 ENCODING='%s'%s", dbname, encoding,
-						 (nolocale) ? " LC_COLLATE='C' LC_CTYPE='C'" : "");
+						 (nolocale) ? " LOCALE='C'" : "");
 	else
 		psql_add_command(buf, "CREATE DATABASE \"%s\" TEMPLATE=template0%s", dbname,
-						 (nolocale) ? " LC_COLLATE='C' LC_CTYPE='C'" : "");
+						 (nolocale) ? " LOCALE='C'" : "");
 	psql_add_command(buf,
 					 "ALTER DATABASE \"%s\" SET lc_messages TO 'C';"
 					 "ALTER DATABASE \"%s\" SET lc_monetary TO 'C';"