input-sys: Prevent braking API changes between 1.28 and 1.29 features

1.28 changes were not published yet, so I'll just retroactively adjust
the older version even tho upstream did technically break the API on us

Author: PolyMeilex

input-sys/include/libinput.1.28.0.h

@@ -5775,7 +5775,7 @@ enum libinput_config_accel_type {
 enum libinput_config_status
 libinput_config_accel_set_points(struct libinput_config_accel *accel_config,
 				 enum libinput_config_accel_type accel_type,
-				 double step, size_t npoints, double *points);
+				 double step, size_t npoints, const double *points);
 
 /**
  * @ingroup config

input-sys/src/bindings/gen_1_28.rs

@@ -1704,7 +1704,7 @@ extern "C" {
         accel_type: libinput_config_accel_type,
         step: f64,
         npoints: usize,
-        points: *mut f64,
+        points: *const f64,
     ) -> libinput_config_status;
 }
 extern "C" {