Sign MacOS releases or update Mac Signing certs for Catalina

[aaroncrespo]

The current preview cannot be used on Mac because it is not signed correctly. (at least for Catalina)

[mjcheetham]

Thanks for reporting this @aaroncrespo.

The binaries & installer are codesigned but not notarised, which is causing the problem on Catalina where it is now mandatory.

[mjcheetham]

@aaroncrespo please can you try the latest release? This version should now be both signed and notarized.

https://github.com/microsoft/Git-Credential-Manager-Core/releases/tag/v2.0.87-beta