`passing/sub-pointer-writeback.pre` is incorrect.

[python-processing-unit]

According to the specification section 5.4:

When a built-in operator produces a transformed value from one or more operand arguments, any operand argument that is a pointer literal MUST be written back through the alias for that operand. Arguments that act only as flags, modes, delimiters, bounds, or other control inputs MUST NOT be written back unless they are themselves part of the transformed output.

The test passing/sub-pointer-writeback.pre requires that SUB write back a pointer subtrahend, even though that is a control input, and not the operand being transformed.