Stop artifact signing when the certificate is expired

**Describe the bug** Our artifact signing certificate is expired and we are in the process of renewing it. It would be nice if the signing would stop directly if it detects that the certificate is no longer valid. I am now seeing this in the output: ``` warn: Sign.Core.ICertificateVerifier[0] The certificate is expired. info: Sign.Core.IDataFormatSigner[0] Signing C:\Users\runneradmin\AppData\Local\Temp\cywac2tz.wcz\ywlfdo3r.exe. fail: Sign.Core.IDataFormatSigner[0] Signing failed with error -2146762486. ``` An earlier exit could happen here.