run: Prevent accidentally running with sudo
run: Prevent accidentally running with sudo

It is a common user error to prepend many flatpak commands with sudo
and doing so with run is quite unsafe and can cause issues.

This check simply handles the `sudo flatpak run foo` case and does
not prevent running as root or even running in a shell created by
sudo.

See also #1357

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak