python tests suite fails on windows

The tests suite at https://github.com/google/magika/blob/main/.github/workflows/python-test-suite.yml somehow fails when running it on windows.

Some of the failures are about mypy (rightfully) complaining about the signal module, but even when commenting that out, other issues pop out when running the tests. These include some misdetection-related checks, which is very weird as nothing should change depending on the operating system.

Start with .github/workflows/python-test-suite.yml and reproduce the Python test suite on Windows. Investigate the mypy signal-module failures and the misdetection-related test failures; the work is done when the Windows suite passes without OS-dependent misdetections.

Written by the indexing model from the issue text.