message: gltfpack: Add KHR_materials_transmission extension to the list
  This is required to keep the gltf files valid after prior changes.
diff: @@ -299,6 +299,7 @@ static void process(cgltf_data* data, const char* input_path, const char* output
  bool ext_pbr_specular_glossiness = false;
  bool ext_clearcoat = false;
  + bool ext_transmission = false;
  bool ext_unlit = false;
  bool ext_instancing = false;
  @@ -356,6 +357,7 @@ static void process(cgltf_data* data, const char* input_path, const char* output
  ext_pbr_specular_glossiness = ext_pbr_specular_glossiness || material.has_pbr_specular_glossiness;
  ext_clearcoat = ext_clearcoat || material.has_clearcoat;
  + ext_transmission = ext_transmission || material.has_transmission;
  ext_unlit = ext_unlit || material.unlit;
  }
  @@ -567,6 +569,7 @@ static void process(cgltf_data* data, const char* input_path, const char* output
  {"KHR_texture_transform", settings.quantize && !json_textures.empty(), false},
  {"KHR_materials_pbrSpecularGlossiness", ext_pbr_specular_glossiness, false},
  {"KHR_materials_clearcoat", ext_clearcoat, false},
  + {"KHR_materials_transmission", ext_transmission, false},
  {"KHR_materials_unlit", ext_unlit, false},
  {"KHR_lights_punctual", data->lights_count > 0, false},
  {"KHR_texture_basisu", !json_textures.empty() && settings.texture_ktx2, true},
  