all: use go1.18
Created by: keegancsmith
This bumps go.mod, sg and asdf to use the latest version of go. Other commits have updated us to go1.18, but this is the important one since it affects both our dev env and CI.
Brew ships go 1.18.1 so this should be good to go.
Test Plan
Ran "sg start oss". main dry run on CI.