fix exception with unsupported version (#17088)

Co-authored-by: Chiedo John <2156688+chiedo@users.noreply.github.com>

Author: rachmari

middleware/contextualizers/webhooks.js

@@ -11,6 +11,7 @@ module.exports = async (req, res, next) => {
   // For example, free-pro-team@latest corresponds to dotcom,
   // enterprise-server@2.22 corresponds to ghes-2.22,
   // and github-ae@latest corresponds to ghae
+  if (!allVersions[req.context.currentVersion]) return next()
   const webhookPayloadDir = allVersions[req.context.currentVersion].miscVersionName
 
   const webhookPayloadsForCurrentVersion = webhookPayloads[webhookPayloadDir]