Changed expected function signature of fs_vector_foreach to expect void.

This bring the method in ine with the return type of fs_comment_free().

This avoid the following compiler message:

  comments.c: In function 'fish_sound_comments_free':
  comments.c:426:40: error: cast between incompatible function types from 'void (*)(FishSoundComment *)' {aka 'void (*)(struct _FishSoundComment *)'} to 'int (*)(void *)' [-Werror=cast-function-type]
    426 |   fs_vector_foreach (fsound->comments, (FishSoundFunc)fs_comment_free);
        |                                        ^