clippy: Allow a complex type
clippy: Allow a complex type

Clippy would stop complaining with

  type FilterParseFn<'a, 'i> = &'a dyn Fn(&mut Parser<'i, '_>) -> Result<FilterFunction, ParseError<'i>>;

But that's not easier to read than what there is right now.

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/747>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg