Checking for tenant config throws warning in PHP 7.4 (#688)

Co-authored-by: Jess Carlos <jess.carlos@stepstonegroup.com>

Provider.php

@@ -32,7 +32,7 @@ class Provider extends AbstractProvider
     protected function getAuthUrl($state)
     {
         return $this->buildAuthUrlFromBase(
-            'https://login.microsoftonline.com/'.($this->config['tenant'] ?: 'common').'/oauth2/authorize',
+            'https://login.microsoftonline.com/'.($this->config['tenant'] ?? 'common').'/oauth2/authorize',
             $state
         );
     }