[IAST] Skip failing tests (#6455)

## Summary of changes

Skip two tests that now fail on master. They fail because the endpoint
in the test app they use was removed.

This wasn't spotted in the PR because they are only run on master.

A larger refactoring to fix this is in progress.

tracer/test/Datadog.Trace.Security.IntegrationTests/IAST/AspNetCore2IastTests.cs

@@ -573,6 +573,8 @@ await VerifyHelper.VerifySpans(spansFiltered, settings)
     [Trait("RunOnWindows", "True")]
     public async Task TestIastStoredXssRequest()
     {
+        throw new SkipException("End point missing due to changes in Samples.Security.AspNetCore2 - refactoring in progess to restore");
+
         var filename = "Iast.StoredXss.AspNetCore2." + (IastEnabled ? "IastEnabled" : "IastDisabled");
         if (RedactionEnabled is true) { filename += ".RedactionEnabled"; }
         var url = "/Iast/StoredXss";
@@ -596,6 +598,8 @@ await VerifyHelper.VerifySpans(spansFiltered, settings)
     [Trait("RunOnWindows", "True")]
     public async Task TestIastStoredXssEscapedRequest()
     {
+        throw new SkipException("End point missing due to changes in Samples.Security.AspNetCore2 - refactoring in progess to restore");
+
         var filename = "Iast.StoredXssEscaped.AspNetCore2." + (IastEnabled ? "IastEnabled" : "IastDisabled");
         var url = "/Iast/StoredXssEscaped";
         IncludeAllHttpSpans = true;