[LFRic] [PSyAD] PSyAD no longer computes adjoint of vector assigments properly in PSyclone 3.0

[DrTVockerodtMO]

In testing PSyclone 3.0, we find that forward code that looks like

vector(:) = vector(:) + constant(:) * scalar

where vector and scalar are active no longer adjoints to

do idx = vector_ubound, vector_lbound, -1
  scalar = scalar + constant(idx) * vector(idx)
end do

but instead does

scalar = scalar + constant(:) * vector(:)

which fails to compile. The former behaviour is expected.