Configure Psalm to ignore MissingFile in ApplicationProvider

The error was intriduced by Psalm 4.21 as it now resolves __DIR__.
It's recommended [1] to ignore the error if it happens despite an
existence check for the file.

[1] https://github.com/vimeo/psalm/issues/3886#issuecomment-663585426

src/Providers/ApplicationProvider.php

@@ -52,6 +52,7 @@ final class ApplicationProvider
         }
 
         if (file_exists($applicationPath = __DIR__ . '/../../../../bootstrap/app.php')) { // Applications
+            /** @psalm-suppress MissingFile file is checked for existence */
             $app = require $applicationPath;
         } elseif (file_exists($applicationPath = getcwd() . '/bootstrap/app.php')) { // Local Dev
             $app = require $applicationPath;