protocols: Mention breaking API change

Due to
https://gitlab.freedesktop.org/wayland/wayland-protocols/-/commit/1c57b24ff867eabacb6ecc1e74b1e4d1ccafcf4b,
the generated code here is now an enum instead of a `u32`.

It seems reasonable to make this a breaking change for
`wayland-protocols-*`, but not release a semver bump of
`wayland-client`/`wayland-server`.

wayland-protocols/CHANGELOG.md

@@ -9,6 +9,9 @@
     - `xdg-dialog-v1`
     - `linux-drm-syncobj-v1`
 
+### Breaking changes
+- `set_constraint_adjustment`/`SetConstraintAdjustment` now takes a `ConstraintAdjustment` instead of a u32.
+
 ## 0.31.2 -- 2024-01-29
 
 - Bump wayland-protocols to 1.33