Vram compressed textures not working on iOS export with GLES2

[HEAVYPOLY]

Godot version:
3.2.3 RC6

OS/device including version:
iPad Pro 9.5" 2016
GLES2

Issue description:
on GLES3, Vram compressed textures work as expected.
on GLES2, with prtvc enabled, the textures don't show and I get an debug error on Xcode:

ERROR: Failed loading resource: res://BrushTextures/smudge_01.jpg.
At: core/io/resource_loader.cpp:278:_load() - Condition "found" is true. Returned: RES()
etc

Steps to reproduce:

Minimal reproduction project:

[Calinou]

Duplicate of #38040, #28683 and #28669. This may be fixed by #38076.