Thanks Kovid! We will have to fix this with a new release.
That said, as a simpler workaround right now based on Kovid's approach, just adding an the following environment variable should then work since we can use the certifi certificate that is in this release until we add our own and change Info.plist and add the mozilla cert.
Code:
export SSL_CERT_FILE="/Applications/Sigil.app/Contents/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/certifi/cacert.pem"
That should do effectively the same thing unless we mess up the environment somehow when we launch python plugins.
Also, another workaround could be to do this upfront in the plugin code using info the the python path to extract the correct path to the certificate no matter where the user install Sigil.app on a mac.