Exclusion of DRC Error "invalid_outline" isn't saved.

Description

The exclusion of the DRC error "Board has malformed outline (no edges found on Edge.Cuts layer)" isn't saved.

It seems to be only this very specific error type which isn't saved. Other types like "not a closed shape" or "self-intersecting" are saved.

Steps to reproduce

1. Create an empty project
2. Place two rectangles on Edge.Cuts layer, make sure they have the same height (else it's an different error) and place them so that the right edge of rectangle one is placed on the left edge of rectangle two. (see screenshot)
3. Run DRC and exclude reported error.
4. Save and close Kicad.
5. Reopen Kicad and the project. The exclusion is gone.

KiCad Version

Application: KiCad x86_64 on x86_64

Version: 7.0.7-2.fc37, release build

Libraries:
	wxWidgets 3.2.1
	FreeType 2.12.1
	HarfBuzz 5.2.0
	FontConfig 2.14.1
	libcurl/7.85.0 OpenSSL/3.0.9 zlib/1.2.12 brotli/1.0.9 libidn2/2.3.4 libpsl/0.21.1 (+libidn2/2.3.3) libssh/0.10.5/openssl/zlib nghttp2/1.51.0

Platform: Fedora release 37 (Thirty Seven), 64 bit, Little endian, wxGTK, gnome-xorg, x11

Build Info:
	Date: Aug 14 2023 00:00:00
	wxWidgets: 3.2.1 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.78.0
	OCC: 7.6.3
	Curl: 7.85.0
	ngspice: 40
	Compiler: GCC 12.3.1 with C++ ABI 1017

Build settings:
	KICAD_SPICE=ON