Fix WebP dealloc method definitions

[Yay295]

This fixes

  src/_webp.c:494:5: warning: cast between incompatible function types from ‘PyObject * (*)(PyObject *)’ {aka ‘struct _object * (*)(struct _object *)’} to ‘void (*)(PyObject *)’ {aka ‘void (*)(struct _object *)’} [-Wcast-function-type]
    494 |     (destructor)_anim_encoder_dealloc, /*tp_dealloc*/
        |     ^

Or to put that a bit more clearly, the function type of the destructor functions should be void (*)(PyObject *) not PyObject * (*)(PyObject *).

[radarhere]

I'm having trouble finding that warning in our CI jobs. Can you find it in one of them and provide a link? If not, what environment are you on?

[Yay295]

Just running locally. I added -Wall -Wextra to my makefile.

[radarhere]

Ok, running that on Linux generates the warning - https://github.com/radarhere/Pillow/actions/runs/3561838551/jobs/5983089664#step:7:2329

And your change here removes it.