Failed test "test_dpi_ratio_change" in test_backend_gl.py

[karlwessel]

The test fails with:

>           assert fig.dpi == 240
E           assert 360 == 240
E            +  where 360 = <Figure size 1800x720 with 0 Axes>.dpi

tests/test_backend_gl.py:252: AssertionError

The same test works for test_backend_qt.py so it has to be some problem with the dpi (which doesn't really work yet anyway) introduced by the gl backend.