docs: enforce that api docs are up-to-date - #540

Merging main has created a CI error.

It looks like the failing test involves installing futures >= 3.1 which is a backport package and does not work on Python 3. If this CI error has just shown up now, maybe the CI instance's default Python has changed?

Edit: Looks like example .egg should be regen'd, because it's got some dead code.

    # Note: this .egg file can be regenerated using zipper:
    # $ third_party/ijar/zipper Cc \
    #   examples/py_import/helloworld.egg \
    #   examples/py_import/helloworld.py=examples/legacy_pip_import/helloworld/helloworld.py \
    #   examples/__init__.py= \
    #   examples/py_import/__init__.py=

I don't understand if the main branch is green, how the futures problem is just happening now. I'll try a rebase just to roll the dice