false positives on shaping-arabic-diacritics-001

[frivoal]

css/css-text/shaping/shaping-arabic-diacritics-001.html passes as a reftest even in browsers that do not comform to the test's expectation.

Firefox nightly 79 (2020-06-08) passes correctly, as per the description.
But Firefox stable 77.0.1, Safari and Chrome all pass, even though the rendering doesn't match the description.

I suspect that might be meant to capture some of that, but it too passes in safari even though the rendering on -001 is wrong.

Not entirely sure how to tweak those tests, but tests passing when the condition isn't fulfilled isn't great.

@jfkthame I think these tests are from you, can you have a look?