File > Append board duplicates Pre-defined item widths

When doing "File > Append board", kicad duplicates Pre-defined item widths.

Description

When doing "File > Append board", kicad duplicates Pre-defined item widths. Expect that Kicad will not duplicate existing pre-defined sizes when Appending board.

Steps to reproduce

1. Run PCB Editor standalone
2. Append existing board
3. Check Board setup > Desing rules > Pre-defined sizes

KiCad Version

Application: KiCad PCB Editor (64-bit)

Version: (6.0.6), release build

Libraries:
	wxWidgets 3.1.6
	libcurl/7.82.0-DEV Schannel zlib/1.2.12

Platform: Windows 10 (build 19044), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Jun 18 2022 23:26:20
	wxWidgets: 3.1.6 (wchar_t,wx containers)
	Boost: 1.79.0
	OCC: 7.6.0
	Curl: 7.82.0-DEV
	ngspice: 37
	Compiler: Visual C++ 1929 without C++ ABI

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON