Unsupported packages architecture warning
This solution is specific for Ubuntu Bionic Beaver (18.xx)
In case if repository contains unsupported platform packages (in this case 32bit packages), during
apt update you will see warning message:
N: Skipping acquire of configured file 'nginx/binary-i386/Packages' as repository 'http://nginx.org/packages/mainline/ubuntu bionic InRelease' doesn't support architecture 'i386'
To fix warning edit source list file by adding
[arch=amd64] to it:
deb [arch=amd64] http://nginx.org/packages/mainline/ubuntu bionic nginx