Run the tests unconditionally and skip if the shaper is not available.
This fixes distcheck (https://github.com/harfbuzz/harfbuzz/pull/3504)
and shows SKIP for these tests instead of ignoring them.
Test that both NFC and NFD input produces identical results for fonts
that used composed fonts internally (Amiri here) and fonts that
decompose internally (Noto Nastaliq Urdu here) and that for the former
composed forms are used.
See https://github.com/harfbuzz/harfbuzz/issues/3179