Fix bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)

When I create a Proxmox pct container running Ubuntu 20.04, it usually gives me this bash warning when I SSH into it for the first time.

bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)

Here is the fix.

sudo locale-gen en_US.UTF-8
sudo mv /etc/default/locale /etc/default/locale.old
sudo echo "LANG=en_US.UTF-8" > /etc/default/locale