Symbol Editor: Checker not reporting on duplicate pin numbers

Description

When creating a symbol in symbol editor, the checker is not detecting if duplicate pin numbers are used.

Steps to reproduce

1. Open HM5118160 symbol
2. Run checker - no issues are found (Pin 28 is duplicated - Vcc and A9)

dram.kicad_sym

KiCad Version

Application: KiCad Symbol Editor

Version: 6.0.5-a6ca702e91~116~ubuntu22.04.1, release build

Libraries:
	wxWidgets 3.0.5

Platform: Linux 5.15.0-30-generic x86_64, 64 bit, Little endian, wxGTK, ubuntu, wayland

	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.74.0
	OCC: 7.5.2
	Curl: 7.83.0
	ngspice: 36
	Compiler: GCC 11.2.0 with C++ ABI 1016

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON