`inplace` does not work in test suite

[scop]

          I wonder if this triggers a bug somewhere, test suite or `inplace` implementation, or my understanding of it?

Debugger entered--Lisp error: (error "Formatter robotidy modified original file in place")

Originally posted by @scop in https://github.com/radian-software/apheleia/pull/263#discussion_r1405410216