Further weaken new pg_createsubscriber test on Windows.

Also omit backslashes (\) in the generated database names on Windows.
As before, perhaps we can revert this after updating affected
buildfarm animals.

Discussion: https://postgr.es/m/2509767.1719773880@sss.pgh.pa.us

src/bin/pg_basebackup/t/040_pg_createsubscriber.pl

@@ -30,8 +30,9 @@ sub generate_db
 
 	$dbname .= $suffix;
 
-	# Old IPC::Run mis-quotes command line arguments containing '"' on Windows
-	$dbname =~ tr/\"//d if ($windows_os);
+	# On Windows, older IPC::Run versions can mis-quote command line arguments
+	# containing double quote or backslash
+	$dbname =~ tr/\"\\//d if ($windows_os);
 
 	$node->command_ok(
 		[ 'createdb', $dbname ],