fix false psalm report

Signed-off-by: szaimen <szaimen@e.mail.de>

php/src/Docker/DockerActionManager.php

@@ -431,6 +431,9 @@ class DockerActionManager
             $tagArray = explode(':', $output['Config']['Image']);
             $tag = $tagArray[1];
             apcu_add($cacheKey, $tag);
+            /**
+             * @psalm-suppress TypeDoesNotContainNull
+             */
             if ($tag === null) {
                 error_log("No tag was found when getting the current channel. You probably did not follow the documentation correctly. Changing the channel to the default 'latest'.");
                 $tag = 'latest';