Fix parsing left/right-assoc kore terms in kast

[gtrepta]

fixes: #3634

[gtrepta]

@radumereuta This is a very small fix, but would you like a test for this?

[radumereuta]

Last time I had to modify that file, I added a test: #2766
Maybe you can modify an existing one to account for this case. That way we don't add to the CI time but we test for the problem.

[gtrepta]

@radumereuta I found a good place for it. Ready for approval.

[virgil-serbanuta]

Thanks!