Saving DXT1 Not implemented! (Portal 2 export crash)

[ThaBluNate]

BEE2 version: 4.40.2
(i also tried a version that was compiled from src that also didn't work)

Description of the bug:
if you export to portal 2 it crashes

Steps to reproduce:
Try to export to portal 2 AT ALL
(i have even tried by just getting a new beemod install and just exporting)

Error log:

Traceback (most recent call last):
  File "app\UI.py", line 829, in export_editoritems
  File "app\gameMan.py", line 698, in export
  File "packages\signage.py", line 221, in export
  File "packages\signage.py", line 295, in build_texture
  File "srctools\vtf.py", line 842, in save
  File "srctools\_py_vtf_readwrite.py", line 129, in save
NotImplementedError: Saving DXT1 not implemented!

[Konclan]

Duplicate of #1660