release 3.9.0 process: reduce warnings (#279)

* fix(riseupvpn): address gofmt warning

Thanks to https://goreportcard.com/report/github.com/ooni/probe-cli.

* fix(utils.go): correct the docu-comment

Thanks to https://goreportcard.com/report/github.com/ooni/probe-cli

* fix: improve spelling

Thanks to https://goreportcard.com/report/github.com/ooni/probe-cli

* fix(modelx_test.go): avoid inefassign warning

Thanks to https://goreportcard.com/report/github.com/ooni/probe-cli

* fix: reduce number of ineffective assignments

Thanks to https://goreportcard.com/report/github.com/ooni/probe-cli

internal/engine/experiment/tlstool/internal/splitter.go

@@ -29,7 +29,6 @@ func SNISplitter(input []byte, sni []byte) (output [][]byte) {
 	}
 	if len(buf) > 0 {
 		output = append(output, buf)
-		buf = nil
 	}
 	output = append(output, input[idx+len(sni):])
 	return