Dont use more than 2000 chars for slack attachments field

src/Monolog/Handler/Slack/SlackRecord.php

@@ -223,7 +223,7 @@ class SlackRecord
     private function generateAttachmentField(string $title, $value): array
     {
         $value = is_array($value)
-            ? sprintf('```%s```', $this->stringify($value))
+            ? sprintf('```%s```', substr($this->stringify($value), 0, 1990))
             : $value;
 
         return array(