Update workflow to mac-os 12

Will likely cause an error when trying to write into keychain as explained in 
https://github.com/FiloSottile/mkcert/issues/94

Maybe running (except in our case it would be System.keychain)

```console
security unlock-keychain /Library/Keychains/System.keychain
```

could do the trick as explained in https://stackoverflow.com/a/50538785