There seems to be some confusion here. The GIL is not an invariant of Python that makes your code thread safe. Python is not altering the deal. You can still use threads to write concurrent code in Python today, and you'll still run into all of the classic concurrency related bugs.
People just mostly don't bother writing threaded code in Python today because it provides no performance benefit. That may change, and it very likely will expose many threading bugs that already exist in many libraries that just have never been found.
You're right, the GIL certainly doesn't automatically make all code thread-safe. However, it does make some operations that would normally be problematic in a multithreaded context thread-safe. Such as: appending to a list, updating a dict, modifying object attributes, and others.
People just mostly don't bother writing threaded code in Python today because it provides no performance benefit. That may change, and it very likely will expose many threading bugs that already exist in many libraries that just have never been found.