Update test after change in HTTP method

Author: stevejgordon

tests/Tests/XPack/MachineLearning/PreviewDataFeed/PreviewDataFeedApiTests.cs

@@ -22,7 +22,7 @@ public PreviewDatafeedApiTests(MachineLearningCluster cluster, EndpointUsage usa
 		protected override object ExpectJson => null;
 		protected override int ExpectStatusCode => 200;
 		protected override Func<PreviewDatafeedDescriptor, IPreviewDatafeedRequest> Fluent => f => f;
-		protected override HttpMethod HttpMethod => HttpMethod.GET;
+		protected override HttpMethod HttpMethod => HttpMethod.POST;
 		protected override PreviewDatafeedRequest Initializer => new PreviewDatafeedRequest(CallIsolatedValue + "-datafeed");
 		protected override bool SupportsDeserialization => false;
 		protected override string UrlPath => $"/_ml/datafeeds/{CallIsolatedValue}-datafeed/_preview";

tests/Tests/XPack/MachineLearning/PreviewDataFeed/PreviewDataFeedUrlTests.cs

@@ -12,7 +12,7 @@ namespace Tests.XPack.MachineLearning.PreviewDataFeed
 {
 	public class PreviewDatafeedUrlTests : UrlTestsBase
 	{
-		[U] public override async Task Urls() => await UrlTester.GET("/_ml/datafeeds/datafeed_id/_preview")
+		[U] public override async Task Urls() => await UrlTester.POST("/_ml/datafeeds/datafeed_id/_preview")
 			.Fluent(c => c.MachineLearning.PreviewDatafeed<Metric>("datafeed_id", p => p))
 			.Request(c => c.MachineLearning.PreviewDatafeed<Metric>(new PreviewDatafeedRequest("datafeed_id")))
 			.FluentAsync(c => c.MachineLearning.PreviewDatafeedAsync<Metric>("datafeed_id", p => p))