Fix string literals that were supposed to be f-strings (#17615)
Summary of the issue:
A couple of strings introduced in the message dialog API work were supposed to be f-strings, but the f prefix was missed, making them string literals.
Description of development approach
Changed the erroneous strings to f-strings.
Testing strategy:
Created a MessageDialog in the python console and ensured the debug and exception messages were output correctly.
Known issues with pull request:
None
