allows custom formatters for slack driver (#26377)

Author: dpsarrou

src/Illuminate/Log/LogManager.php

@@ -273,7 +273,7 @@ protected function createSlackDriver(array $config)
                 $this->level($config),
                 $config['bubble'] ?? true,
                 $config['exclude_fields'] ?? []
-            )),
+            ), $config),
         ]);
     }