typing_extensions missing in requirements

[t1h0]

8e95c71 added usage of typing_extensions to pipeline.py. Specifically, cast() is used which is only available in typing_extensions>=4.7.0. As typing_extensions is not a requirement to news-please, the solution to the issue is one of the following pull requests:

• Raise typing-extensions and python version #276: Adding typing_extensions>=4.7.0 as a requirement, however necessarily also raising the python version to 3.7+

or

• Remove typing_extensions.cast #277: Removing the usage of cast (as it is for type checking only and not needed anyway as far as I can tell)

EDIT: Newspaper4k (required by news-please) runs on python 3.8+. news-please should therefore be raised to 3.8 anyway so the first solution might be the best one.

[fhamborg]

thanks! fixed it with the help of your changes from #276