try to fix tests

Author: pwelter34

test/FluentRest.Tests/FluentEchoTests.cs

@@ -255,7 +255,7 @@ public async Task EchoPostData()
         Assert.Equal(user.FirstName, result.Json.Value.GetProperty("firstName").GetString());
     }
 
-    //[Fact]
+    [Fact]
     public async Task EchoPostRawJsonContent()
     {
         var user = UserData.Create();

test/FluentRest.Tests/HostFixture.cs

@@ -28,6 +28,9 @@ public async Task InitializeAsync()
     {
         await _container.StartAsync();
 
+        // wait for startup
+        await Task.Delay(5000);
+
         // get container url
         HttpBinUrl = $"http://{_container.Hostname}:{_container.GetMappedPublicPort(80)}";
     }