Re-enable GetAsync_LargeHeader_Success for H/3 (#57955)

Fixes #55508

Author: CarnaViire

src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Headers.cs

@@ -214,12 +214,6 @@ await LoopbackServerFactory.CreateClientAndServerAsync(async uri =>
         [InlineData("RandomCustomHeader", 12345)]
         public async Task GetAsync_LargeHeader_Success(string headerName, int headerValueLength)
         {
-            if (UseVersion == HttpVersion.Version30)
-            {
-                // [ActiveIssue("https://github.com/dotnet/runtime/issues/55508")]
-                return;
-            }
-
             var rand = new Random(42);
             string headerValue = string.Concat(Enumerable.Range(0, headerValueLength).Select(_ => (char)('A' + rand.Next(26))));