Test only 3.9 and 3.11 ; build only in 3.11

Created by: scarlehoff

Since we are not compiling anymore, we only need the noarch package and so we only need to upload one package to the server every time we merge from master (instead of six).

For the tests, at the moment I've left 4: 3.9, 3.11 and ubuntu/mac. We are back to 4 tests with conda (+2 in python). We can get away with less of course. I just want to avoid the many false positives that we get when the server in Milan stops accepting connections because we are downloading too much stuff too quickly.