Fix format specifier warning in importImagePixels

[botanegg]

Changed %ld to %zu for PHP_VERSION_ID >= 70000, coz map_len is size_t now

Prevent next warings on 32bit systems
https://gitlab.alpinelinux.org/botanegg/aports/-/jobs/1958641#L325

/builds/botanegg/aports/community/php84-pecl-imagick/src/imagick-3.8.0/imagick_class.c:2428:92: warning: format '%ld' expects argument of type 'long int', but argument 4 has type 'size_t' {aka 'unsigned int'} [-Wformat=]
 2428 |                                 "The map contains incorrect number of elements. Expected %ld, array has %u",
      |                                                                                          ~~^
      |                                                                                            |
      |                                                                                            long int
      |                                                                                          %d
......
 2432 |                                 (width * height) * map_len,
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~                                  
      |                                                  |
      |                                                  size_t {aka unsigned int}