[tests] Assert.Inconclusive() tests with http errors

[jonathanpeppers]

MSBuild tests using DownloadedCache can randomly fail with HTTP errors such as:

System.Net.Http.HttpRequestException : Response status code does not indicate success: 504 (Gateway Time-out).
Stack trace
at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
at Xamarin.ProjectTools.DownloadedCache.GetAsFile(String url, String filename) in /Users/runner/work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/DownloadedCache.cs:line 39
at Xamarin.ProjectTools.BuildItem.<>c__DisplayClass70_0.<set_WebContent>b__0() in /Users/runner/work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/BuildItem.cs:line 309
at Xamarin.ProjectTools.XamarinProject.<>c.<Save>b__110_0(BuildItem s) in /Users/runner/work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/XamarinProject.cs:line 455
at System.Collections.Generic.List`1.AddRange(IEnumerable`1 collection)
at Xamarin.ProjectTools.XamarinProject.Save(Boolean saveProject) in /Users/runner/work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/XamarinProject.cs:line 455
at Xamarin.ProjectTools.ProjectBuilder.Save(XamarinProject project, Boolean doNotCleanupOnUpdate, Boolean saveProject) in /Users/runner/work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/ProjectBuilder.cs:line 98
at Xamarin.ProjectTools.ProjectBuilder.Build(XamarinProject project, Boolean doNotCleanupOnUpdate, String[] parameters, Boolean saveProject, Dictionary`2 environmentVariables) in /Users/runner/work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/ProjectBuilder.cs:line 128
at Xamarin.Android.Build.Tests.BindingBuildTest.BindngFilterUnsupportedNativeAbiLibraries(AndroidRuntime runtime) in /Users/runner/work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BindingBuildTest.cs:line 411
at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
at System.Reflection.MethodBaseInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs, BindingFlags invokeAttr)

Let's call Assert.Inconclusive() when we catch such exceptions, so that the test is marked as inconclusive instead of failed.

We also log information about the exception.