gdiplus/tests: Don't fail if Microsoft Sans Serif and Times New Roman are not installed.

[Vincent Povirk]

> It's a bit what the test was trying to do with Microsoft Sans Serif
> except that I also take exception with the todo_wine since the fix is
> not to change Wine but to install the missing font.

I'm not too concerned about what happens in this case, but one
alternative would be to always test that the function successfully
returns a font but only test that the font is what we expect when that
font is installed.