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)