Further further fix pg_upgrade crossversion test for adminpack.

Apparently, buildfarm animal crake has the adminpack regression DB
named as "regression_adminpack" in some branches.  Not clear why
I didn't see that when testing here.  In any case, drop that too.

Discussion: https://postgr.es/m/0CFB76D0-0510-48B2-9916-1199F93BC28C@yesql.se

src/test/perl/PostgreSQL/Test/AdjustUpgrade.pm

@@ -111,7 +111,10 @@ sub adjust_database_contents
 	{
 		_add_st($result, 'postgres',
 			'drop database if exists contrib_regression_adminpack');
+		_add_st($result, 'postgres',
+			'drop database if exists regression_adminpack');
 		delete($dbnames{'contrib_regression_adminpack'});
+		delete($dbnames{'regression_adminpack'});
 	}
 
 	# we removed this test-support function in v17