The spec for .usdz permits only a small handful of file formats to be
contained in the archive, and HDR is not among those supported[1]. This
also causes validation errors with the `usdchecker` tool (will be
properly tested in a follow up change).
Ignoring the potential for a user to export a .usdz file with materials
referencing unsupported file formats, Blender itself should use only
the supported formats for its business.
[1] https://openusd.org/release/spec_usdz.html#usdz-specification
Pull Request: https://projects.blender.org/blender/blender/pulls/144101
2822b3badf