chore: update to use Go 1.20

[BobyMCbobs]

update to use Go 1.20

related: https://github.com/GeoNet/tickets/issues/13645

[wilsonjord]

Replacing ioutil to use the functionality provided by io and os packages should be fairly easy; a quick scan of the code reveals:

fdsn-ws/fdsn_event.go
113:    fdsnEventIndex, err = ioutil.ReadFile("assets/fdsn-ws-event.html")

fdsn-ws/fdsn_station.go
130:    fdsnStationIndex, err = ioutil.ReadFile("assets/fdsn-ws-station.html")
485:            body, err := ioutil.ReadAll(r.Body)

fdsn-ws/server_test.go
71:             log.SetOutput(ioutil.Discard)

fdsn-ws/fdsn_dataselect.go
64:     fdsnDataselectIndex, err = ioutil.ReadFile("assets/fdsn-ws-dataselect.html")

fdsn-quake-consumer/sc3ml_backload_test.go
40:     files, err := ioutil.ReadDir(dir)
73:                             b, err = ioutil.ReadFile(f)

fdsn-quake-consumer/sc3ml_test.go
20:             b, err := ioutil.ReadFile("etc/" + input)
100:                    b, err := ioutil.ReadFile("etc/" + input)
122:            b, err := ioutil.ReadFile("etc/" + input)
151:    if b, err = ioutil.ReadAll(f); err != nil {
176:    if b, err = ioutil.ReadAll(f); err != nil {

fdsn-ws-nrt/routes_test.go
80:             log.SetOutput(ioutil.Discard)

fdsn-ws-nrt/fdsn_dataselect.go
41:     fdsnDataselectIndex, err = ioutil.ReadFile("assets/fdsn-ws-dataselect.html")

Deployment and post-deployment checks would need to be done. Perhaps I can do this as a sort of test case @junghao ?

[BobyMCbobs]

@wilsonjord, got the same thing here for GeoNet/kit https://github.com/GeoNet/kit/pull/140#issuecomment-1608646526

[BobyMCbobs]

closing for now. It would be suitable to be done when the team is ready