Fixes certificate for GHE Internal ELB

To be tagged v1.20.12

base/github/elbclassic.tf

@@ -98,7 +98,7 @@ resource "aws_elb" "internal" {
         instance_protocol  = "HTTPS"
         lb_port            = 443
         lb_protocol        = "HTTPS"
-        ssl_certificate_id = aws_acm_certificate.cert_public.arn
+        ssl_certificate_id = aws_acm_certificate.cert.arn
     }
 
     listener {
@@ -106,7 +106,7 @@ resource "aws_elb" "internal" {
         instance_protocol  = "HTTPS"
         lb_port            = 8443
         lb_protocol        = "HTTPS"
-        ssl_certificate_id = aws_acm_certificate.cert_public.arn
+        ssl_certificate_id = aws_acm_certificate.cert.arn
     }
 
     listener {