All these files should be sourced, not executed; and Debian's lintian complains: W: zsh-syntax-highlighting: script-not-executable usr/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh
This was broken by c2b9327b07 and tracked as zsh-users/zsh-syntax-highlighting#199. This fixes the vanilla-newline.zsh test, which was was (consciously) broken by the previous commit.
c2b9327b07