Run code analysis on fbs handler

Author: jekuaitk

CHANGELOG.md

@@ -11,6 +11,8 @@ before starting to add changes. Use example [placed in the end of the page](#exa
 
 ## [Unreleased]
 
+- Adds missing `http-message-util` requirement and use statement.
+
 ## [3.21.1] 2025-01-06
 
 - Updated Maestro notification handler assignment message format.

phpstan.neon

@@ -2,6 +2,7 @@ parameters:
   level: 6
   paths:
     - modules/os2forms_digital_post/
+    - modules/os2forms_fbs_handler/
   excludePaths:
     # @see https://github.com/mglaman/drupal-check/issues/261#issuecomment-1030141772/
     - vendor