Field values are case insensitive

Should address "HTTP cache must not use a cached response with
Cache-Control: No-CaChE, even with max-age and Expires" from
https://cache-tests.fyi.

bin/varnishd/builtin.vcl

@@ -156,9 +156,9 @@ sub vcl_backend_response {
         return (deliver);
     } else if (beresp.ttl <= 0s ||
       beresp.http.Set-Cookie ||
-      beresp.http.Surrogate-control ~ "no-store" ||
+      beresp.http.Surrogate-control ~ "(?i)no-store" ||
       (!beresp.http.Surrogate-Control &&
-        beresp.http.Cache-Control ~ "no-cache|no-store|private") ||
+        beresp.http.Cache-Control ~ "(?i:no-cache|no-store|private)") ||
       beresp.http.Vary == "*") {
         # Mark as "Hit-For-Miss" for the next 2 minutes
         set beresp.ttl = 120s;