Revert "Set TLS minimum version to 1.3 for Ingress to Activator (knat…

…ive#14074)"

This reverts commit 8ea1cb6.

cmd/activator/main.go

@@ -285,7 +285,7 @@ func main() {
 		name, server := "https", pkgnet.NewServer(":"+strconv.Itoa(networking.BackendHTTPSPort), ah)
 		go func(name string, s *http.Server) {
 			s.TLSConfig = &tls.Config{
-				MinVersion:     tls.VersionTLS13,
+				MinVersion:     tls.VersionTLS12,
 				GetCertificate: certCache.GetCertificate,
 			}
 			// Don't forward ErrServerClosed as that indicates we're already shutting down.