Don't pass -y to paru (no system upgrade)

[notlesh]

This PR makes a one-char change (no -y to paru) so that it will not perform a system upgrade.

The practical effect of this is that running ./install to invoke dotbot will not attempt to do a system upgrade.

My rationale for this is:

• It consumes time and other resources to do this; I may not want to do that just to run ./install
• It can introduce errors that otherwise wouldn't occur (e.g. introduce a package conflict). This particular case causes a hard-to-diagnose issue where ./install will error without any useful output (even with -vv).

[notlesh]

Oops, this was meant to go against my own fork, not here. But I might as well leave this up in case it's interesting :)