Fix icu tests with C locale

Similar to 1e08576691, but for the icu
test suite.

Reported-by: Christoph Berg <myon@debian.org>
Discussion: https://www.postgresql.org/message-id/YyWeU61YMFwjVdxE@msg.df7cb.de

src/test/icu/t/010_database.pl

@@ -54,7 +54,7 @@ b),
 # Test error cases in CREATE DATABASE involving locale-related options
 
 my ($ret, $stdout, $stderr) = $node1->psql('postgres',
-	q{CREATE DATABASE dbicu LOCALE_PROVIDER icu TEMPLATE template0});
+	q{CREATE DATABASE dbicu LOCALE_PROVIDER icu TEMPLATE template0 ENCODING UTF8});
 isnt($ret, 0,
 	"ICU locale must be specified for ICU provider: exit code not 0");
 like(