gnome-help: Fix typos catched by codespell ci job
These are just comments, so they are harmless typos, but I rather fix them to allow our CI job to succeed onwards.
See https://gitlab.gnome.org/GNOME/gnome-user-docs/-/jobs/2561791
$ codespell -S ".png,.po,.git,.jpg" -f --skip=".po,./NEWS,./gnome-help/Makefile.am" ./gnome-help/C/keyboard-layouts.page:128: copping ==> coping, copying, cropping ./gnome-help/C/net-wired-connect.page:31: overlayed ==> overlaid