chromium displays "Cannot update Chromium" notification... can't suppress.

[Art Botterell]

Using chromium-browser in kiosk mode, every day or so the screen gets a popup saying "Cannot update Chromium" and asking the user to click a button to reload Chromium. This seems to be the same as Debian bug 944443668 (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=943668) but Debian marked that as fixed in Chromium version 78.0.3904.97-1... and now I'm seeing it on buster in Chromium v. 78-3904.108.

This is a show-stopper for a kiosk application, as it not only disrupts the UX but both encourages and enables untrained users to change the software configuration.

I'm invoking Chromium thus:

/usr/bin/chromium-browser --app=http://127.0.0.1:8911 --check-for-update-interval=604800 --disable-component-update --disable-session-crashed-bubble --kiosk --noerrdialogs --disable-translate --no-first-run --fast --fast-start --disable-infobars --disable-features=TranslateUI --disk-cache-dir=/dev/null --password-store=basic