Fix upgrade code-server.service in install script

[jsjoeio]

Oh just saw this does not use our install script. In that case use -U instead of -i. But we do need to also fix our install script.

Fix install script for upgrading when using the code-server.service

Originally reported here: #4316 (reply in thread)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no activity occurs in the next 5 days.

[jsjoeio]

Not stale

[code-asher]

Fixed a while back, turns out you can just always use -U and it will install if not yet installed.