fix incorrect as usage in MessageReceiver

[SimonCropp]

Fixes #
Design discussion issue #

Changes

as should only be used when unsure of the type and then a null check must follow it. in this case i assume since there is no null check, the type is therefore known, and a direct cast will prevent a potential null ref exception

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.39%. Comparing base (89ea5c6) to head (8989b3f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6105   +/-   ##
=======================================
  Coverage   86.39%   86.39%           
=======================================
  Files         257      257           
  Lines       11640    11640           
=======================================
  Hits        10056    10056           
  Misses       1584     1584