Gltf-blender-io: T64760 : Alpha export regression

[julienduroure]

Bug from blender repo:
https://developer.blender.org/T64760

[SurlyBird]

@julienduroure Any ETA on a fix for this?

[julienduroure]

@donmccurdy @emackey :

I didn't work on exporting material yet, maybe yo ucan have a look on it?
Seems to be a regression. It is not working anymore on 0.9.4, but works on version (before we include version in asset generator string)

[julienduroure]

Note: Generated image has no alpha channel

[SurlyBird]

I can fix glTF exports by simply repacking the texture (with alpha) in VS Code, so I'm not blocked, but I definitely would love to see the return of the correct functionality. Thanks for all the hard work on this.

[julienduroure]

@emackey : This seems to be linked to texture export you commited/you are involved on. Do you have any time to have a look on it?

Note: We've got another blender issue open regarding alpha export, that is probably same issue : https://developer.blender.org/T65234

[emackey]

Also reported in #425. I'll take a look.