maybe related to this issue: https://bugs.python.org/issue18831

we can't import a module where the name contains '-', for example

from my-module import my_function

but with importlib.import_module

we can import this module.

import_module does not respect the python syntax for the name of the module, we should avoid that.

1. Add a DeprecationWarning for 3.8+
2. in 3.10, remove this DeprecationWarning and remove the support of the '-' in importlib.import_module