New xcb-proto element `length` not yet handled by xelb

[a02c1175-5220-4e75-b7a1-18e20548305f]

Between xcb-proto version 1.14.1 and 1.15, a new element has been introduced:
https://gitlab.freedesktop.org/xorg/proto/xcbproto/-/commit/c36dde3f4535e948318edc843faeee118492b38e

Here the new element is used:
https://gitlab.freedesktop.org/xorg/proto/xcbproto/-/commit/f0db8b7d31a379fe26f6cc592be997c8ce5f0b2d

This leads to xelb not building anymore:
https://bugs.debian.org/1017294

[medranocalvo]

Thank you. This has been fixed at emacs-exwm/xelb#4.