Move `PyErr_NormalizeException()` up a few lines (#3971)

* Add error_already_set_what what tests, asserting the status quo.

* Move PyErr_NormalizeException() up a few lines.

* @pytest.mark.skipif("env.PYPY") from PR #1895 is required even for this much simpler PR

* Move PyException_SetTraceback() with PyErr_NormalizeException() as suggested by @skylion007

* Insert a std::move() as suggested by @skylion007