SDL_GL_SetSwapInterval (fails after first time): SDL feature or a wrapper bug? about py-sdl2

[LukeMS]

Not sure if it is a SDL feature or a wrapper bug and if there is any need to set swap interval more then once.
For now the test is ignoring the assertion fail after the first swap set:
`

def test_SDL_GL_GetSetSwapInterval(self):
    ...
    for i, swap in enumerate((0, 1)):
        self.assertEqual(video.SDL_GL_LoadLibrary(None), 0)
        window = video.SDL_CreateWindow(b"OpenGL", 10, 10, 10, 10,
                                        video.SDL_WINDOW_OPENGL)
        ctx = video.SDL_GL_CreateContext(window)
        video.SDL_GL_MakeCurrent(window, ctx)

        video.SDL_GL_SetSwapInterval(swap)
        if i == 0:
            # Fix https://github.com/LukeMS/py-sdl2/issues/3

            self.assertEqual(video.SDL_GL_GetSwapInterval(), swap)
    ...

`