Context API: edge-case where chaining fails

[Shoeboxam]

Traceback (most recent call last):
  File "/Users/michael/openDP/openDP/.binder/out/2024/demo-drifting-spaces.py", line 24, in <module>
    subcontext.query().laplace()
  File "/Users/michael/openDP/openDP/python/src/opendp/context.py", line 422, in make
    new_chain = self._chain >> new_chain
                ~~~~~~~~~~~~^^~~~~~~~~~~
TypeError: unsupported operand type(s) for >>: 'tuple' and 'PartialChain'

This is a side-issue that I encountered in the script from #1375