`input` not working in `Ex` mode

[pierreganty]

The following shows it is possible to enter Ex mode but it is not possible to get out of it.

>>> import neovim
>>> n = neovim.attach("child", argv=['/opt/homebrew/bin/nvim', "--clean", "--embed", "--headless"])
>>> n.api.get_mode()
{'mode': 'n', 'blocking': False}
>>> n.input("Q")
1
>>> n.api.get_mode()
{'mode': 'ce', 'blocking': False}
>>> n.input("vi")
2
>>> n.api.get_mode()
{'mode': 'ce', 'blocking': False}
>>> n.input(":vi")
3
>>> n.api.get_mode()
{'mode': 'ce', 'blocking': False}