remove redundat directory separator which caused "//" in path not fou…

…nd errors

src/Psalm/Config.php

@@ -787,7 +787,7 @@ public static function loadFromXMLFile(string $file_path, string $current_dir):
     {
         $file_contents = file_get_contents($file_path);
 
-        $base_dir = dirname($file_path) . DIRECTORY_SEPARATOR;
+        $base_dir = dirname($file_path);
 
         if ($file_contents === false) {
             throw new InvalidArgumentException('Cannot open ' . $file_path);
@@ -1304,15 +1304,15 @@ private static function fromXmlAndPaths(
         // ProjectAnalyzer::getInstance()->check_paths_files is not populated at this point in time
 
         $paths_to_check = null;
-        
+
         global $argv;
 
         // Hack for Symfonys own argv resolution.
         // @see https://github.com/vimeo/psalm/issues/10465
         if (!isset($argv[0]) || basename($argv[0]) !== 'psalm-plugin') {
             $paths_to_check = CliUtils::getPathsToCheck(null);
         }
-        
+
         if ($paths_to_check !== null) {
             $paths_to_add_to_project_files = array();
             foreach ($paths_to_check as $path) {