Pin maximum TF version
# What does this PR do?

We now also depend on `tensorflow-text`, whose minor versions are typically released a few days after new `tensorflow` releases. From tests against the `tensorflow` release candidate, `tensorflow-text`-based functions fail when these two libraries do not have the same version.

This PR pins the maximum TF version so that our CI doesn't break with the upcoming `tensorflow` release. When the corresponding `tensorflow-text` library gets released we should be able to unpin it again.
_The documentation is not available anymore as the PR was closed or merged._<|||||>@ydshieh the CI fail seems unrelated 🤔 do you know potential causes?<|||||>Unfortunately no. Let me find some time to take a look, but I think you are good to merge :-)<|||||>Yes I think that's an unrelated error linked to a new cache being made as the `setup.py` is updated. It's unrelated to the PR, but we need to have a look at what's going on.

Let's merge this PR!

Thanks for your contribution :)