Make sure Y channel is inverted on normal map

[Jigoku]

Tesseract (and cube2?) requires the Y channel of normals to be inverted for things to look as expected;

Most of the nobiax models probably require this change as already noticed with rock_02 and rock_03.

Same check should be made for models in other repos also, particularly where an asset was imported from OpenGameArt etc.

[Jigoku]

• flip Y normal channel nobiax#17 rock_02 & rock_03