If you want a project to appear in https://pkg.go.dev then visit the expected page and click on the "Request ..." button.
e.g.
https://pkg.go.dev/github.com/integralist/go-flags
I clicked on the button "Request github.com/integralist/go-flags" and it started to populate.
https://pkg.go.dev/github.com/fastly/go-fastly/v3@main
or
https://pkg.go.dev/github.com/fastly/go-fastly/v3@v3.8.0 (and there should be a button that will show letting you pull the version specified).
Or yet another way is:
https://sum.golang.org/lookup/github.com/fastly/go-fastly/v3@v3.8.0