System Monitor Freeze Break exception

Hi,

Due to a mistake (commit for 3.30 then reverted) [and a bad memory of the
maintainer - myself - [1] System Monitor is the only core app without an
updated icon.
I would like to fix that, and would request a freeze break exception to
change the application icon in context of the App Icon Redesign [2]
initiative being complete with all core app icons being updated.
The patch should be completely safe, only being an icon change.
The fix consists of removal of the old (fixed-size) icons, and adding new
icons (one scalable and one symbolic), plus the required change in the
desktop file.

[1] https://gitlab.gnome.org/GNOME/gnome-system-monitor/merge_requests/2
[2] https://gitlab.gnome.org/GNOME/Initiatives/issues/2

Regards,
Robert