Switch to SHA256 timestamp signatures to fix build failure

It seems that Sectigo's timestamping server has started failing to provide
timestamping for the default settings. Presumably this is part of their
CA expiry that happened at the end of May? Explicitly requesting SHA256
instead is better, and seems like it's been well supported for years.

Author: pimterry

electron-forge.config.js

@@ -59,7 +59,7 @@ module.exports = {
             path.resolve('./certificates/encrypted-win-cert.pfx')
         }" /p "${
             ELECTRON_FORGE_ELECTRON_WINSTALLER_CONFIG_CERTIFICATE_PASSWORD
-        }" /tr http://timestamp.comodoca.com/`
+        }" /tr http://timestamp.comodoca.com/ /td sha256`
     },
     "electronInstallerDMG": {
         "name": "HTTP Toolkit",