Only Left and returnValue gets checked for dynamic in signature

[jcouv:] the linked PR makes it clearer what the problem is. It just needs a test to verify the impact and fix.

Version Used: Main branch

Steps to Reproduce:

1. I ran a roslyn analyser to check for identical subexpressions on this repo and encountered a diagnostic on this line.
2. I checked to code if this was a correct diagnostic and to me it seemed like a correct diagnostic

Diagnostic Id: IdenticalSubexpression Expected Behavior: No diagnostic from an identical subexpression subexpression Actual Behavior:

I get a diagnostic from an identical subexpression subexpression on this line