CI doesn't recognise type hints in eth2spec

[gurukamath]

The eth2spec library was added as a dependency in cancun since the point_evaluation precompile requires some of its functions. However, mypy fails on CI to recognise the type hints from this library even though the py.typed file was recently added to it. See here. We will need to analyse and correct why this is not recognised on CI. As a temporary fix, a type ignore hint has been added. This will have to be removed once a permanent fix is applied.

Note: mypy did not throw any error upon local execution, so it could just be something specific to CI

[petertdavies]

Fixed by #885