Fix CI on macos

[hhugo]

• The multicast test failure could be caused by add "local network access" permission for macOS 15 runners actions/runner-images#10924
• The getpwuid failure is that the direct unix call returns pw_shell = /bin/bash but the lwt_unix call returns pw_shell = /bin/sh

[raphael-proust]

thanks for the investigation

i don't have access to a macos machine and this is lower priority than other issues for now

i might come around to fixing it later but no timeline for now