upgrade to docify 0.2.6 (#2069)

Updates `docify` to 0.2.6, which fixes a bug that was preventing nesting
`#[docify::export]` within sub-items of items that already have
`#[docify::export]` attached to them from working properly.

Release notes here:
https://github.com/sam0x17/docify/releases/tag/v0.2.6

cc @ggwpez @Kianenigma