Gerber export to PCBnew is old format

Description

When you open GERBER files in Gerbview and then export ( File -> Export to PCB Editor) and then open the pcb file in pcbnew, you are prompted "This file was created by an older version of Kicad. It will be converted to the new format when saved"

Steps to reproduce

1. Launch GerbView-5.99
2. Load GERBERS
3. Export to PCB Editor
4. Load PCBNew-5.99
5. Load previously exported PCB file

KiCad Version

Application: KiCad

Version: (5.99.0-10753-g208dd5cbd5-dirty), release build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.77.0 GnuTLS/3.7.2 (OpenSSL/1.1.1k) zlib/1.2.11 nghttp2/1.43.0

Platform: Linux 5.12.0-gentoo x86_64, 64 bit, Little endian, wxGTK, awesome, x11

Build Info:
	Date: Jun  1 2021 22:41:31
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.76.0
	OCC: 7.5.1
	Curl: 7.77.0
	ngspice: 34
	Compiler: GCC 11.1.0 with C++ ABI 1016

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON