The test code with ignore_tkr(tk) on character dummy passed by
fir.boxchar<> was crashing the compiler in [an
assert](2afe678f0a/flang/lib/Optimizer/Dialect/FIRType.cpp (L632))
in `changeElementType`.
It makes little sense to call changeElementType on a fir.boxchar since
this type is lossy (the shape is not part of it). Just skip it in the
code dealing with ignore(tk) when hitting this case
e6618aae43