use leased buffer for tags when calling SetAsync

# Conflicts:
#	src/Middleware/OutputCaching/src/OutputCacheEntryFormatter.cs

Author: mgravell

src/Middleware/OutputCaching/src/OutputCacheEntryFormatter.cs

@@ -520,7 +520,8 @@ static FrozenDictionary<string, int> BuildCommonHeadersLookup()
                 pairs.Add(new(header, i));
             }
         }
-        return FrozenDictionary.ToFrozenDictionary(pairs, StringComparer.Ordinal);
+
+        return FrozenDictionary.ToFrozenDictionary(pairs, StringComparer.OrdinalIgnoreCase);
     }
 
     internal static bool ShouldStoreHeader(string key) => !IgnoredHeaders.Contains(key);