The GHC issue that caused `JuicyPixels` to fail (ghc/ghc#17590) has
been fixed, so `JuicyPixels` can be removed from the list of expected
failures.

The original issue that caused `free-algebras` to fail
(ghc/ghc#17710) has been fixed, but a new issue has taken its place
(ghc/ghc#16502 (comment 259055)). I've
changed the expected failure reason accordingly.

`singletons` now fails on HEAD due to ghc/ghc#17923, so this patch
also adds it as an expected failure.