Drop support for Python 3.9, 3.8

With https://github.com/Granulate/gprofiler/pull/790 we are fully based on 3.10 now.
This means we can drop support (linting, testing) of old versions, and start using new Python features (e.g I'm tired of `error: "dict" is not subscriptable, use "typing.Dict" instead`).

I'll let the new version post #790 run for a while, and if all is well after a month or so, we'll remove support from the old versions.

Start by reviewing pull request #790 and the Python-version settings for linting and testing. Remove Python 3.8 and 3.9 support while retaining Python 3.10, then verify the lint and test configuration and confirm that the existing test suite passes.

Written by the indexing model from the issue text.