tests: Add ability to test different expected outputs based on Python version. Similar to the previous change, there was also a change in what gets escaped by `urllib.parse.quote` (as in: the tilde sign ('~') stopped being escaped). So now we need to be able to test different outputs in the tests, yay again.

from piecrust.rendering import RenderingContext, render_page


def render_simple_page(page):
    ctx = RenderingContext(page)
    rp = render_page(ctx)
    return rp.content