According to the CSL manual, the default entry spacing is 1.
We were treating it as 0.
T.P.Citeproc: always include an entry-spacing attribute
in the Div if the bibliography element contains an entry-spacing
attribute (previously we omitted it when it was 0).
LaTeX writer: use entry spacing 1 if no entry-spacing
attribute is present.
Update tests.
See #9058.