EnvVar references generate "Unresolved text variable" errors in DRC check

Description

When using a variable in the "Datasheet" field in a footprint (seems to be automatically copied from symbol) the following DRC Error occurs.

Error: Unresolved text variable 
   Datasheet '${KIPRJMOD}/datqasheet/my_component...' of R1

Steps to reproduce

1. Open attached project localDataSheet.zip
2. Open PCB
3. Run DRC
4. Error: Unresolved text variable Datasheet '${KIPRJMOD}/datqasheet/my_component...' of R1

When changing the braces around the variable from {} to () the error is gone.

This seems to be similar to #4644 (closed)

KiCad Version

Application: KiCad x86_64 on x86_64

Version: 8.0.0-8.0.0-1~ubuntu23.10.1, release build

Libraries:
	wxWidgets 3.2.2
	FreeType 2.13.1
	HarfBuzz 8.0.1
	FontConfig 2.14.2

Platform: Ubuntu 23.10, 64 bit, Little endian, wxGTK, X11, ubuntu-xorg, x11

	wxWidgets: 3.2.2 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.74.0
	OCC: 7.6.3
	Curl: 8.2.1
	ngspice: 42
	Compiler: GCC 13.2.0 with C++ ABI 1018

Build settings: