pg_amcheck: Fix test failure on Windows with non-existing role

For SSPI auth extra users need to be explicitly allowed, or we get
"SSPI authentication failed" instead of the expected "role does not
exist" error.

This report also means that the test has never worked on Windows since
its introduction in 9706092839db, because it has always bumped on an
authentication failure rather than an error about the role not existing.

Oversight in eef4a33f62f7, that has added a pattern check on the error
generated by the command.

Per report from Tom Lane, via buildfarm member drongo.

Author: Dagfinn Ilmari Mannsåker
Reviewed-by: Andrew Dunstan
Discussion: https://postgr.es/m/379085.1737734611@sss.pgh.pa.us

src/bin/pg_amcheck/t/002_nonesuch.pl

@@ -11,7 +11,7 @@ use Test::More;
 # Test set-up
 my ($node, $port);
 $node = PostgreSQL::Test::Cluster->new('test');
-$node->init;
+$node->init(auth_extra => [ '--create-role' => 'no_such_user' ]);
 $node->start;
 $port = $node->port;