Context

Fix a bug in the pretty-printing of s-expressions that do not end with E.

Manually testing the MR

Add this to manifest/manifest.ml below let of_atom_list:

  let () = pp Format.std_formatter [ S "l" :: S "a" ]

Before this MR this would print (la), which is incorrect. After this MR this prints (l a), which is correct.

Interestingly [ S "l" :: S "a" :: E ] would work.

Please also check that no existing dune file is modified by make -C manifest.

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Provide automatic testing (see the testing guide).
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