Spurious UnusedElaboratable error if pins aren't locked

[robtaylor]

rm pins.lock
pdm submit

Error while executing `silicon submit`: Lockfile pins.lock not found. Run `chipflow pin lock`
/Users/roberttaylor/Code/ChipFlow/chipflow-lib/chipflow_lib/steps/silicon.py:32: UnusedElaboratable: <amaranth.hdl._dsl.Module object at 0x1073f75d0> created but never used
  m = Module()