I think it isn't a huge deal if an English or French or Social Studies teacher isn't great in math, but is otherwise a good candidate.
But should someone who fails the math proficiency test be a math teacher? Probably not.
Society should try to match everyone with jobs which they are capable of doing, teaching is a good job. We shouldn't unnecessarily exclude people from doing A just because they lack the skills for doing B.
Here is examples of what is on the test:
https://cpl.oise.utoronto.ca/course/mathematics-proficiency-...
Video discussion of the test questions: https://www.youtube.com/watch?v=T-7fnPD_c7w