Use DateParseHandling.None when loading JObject for MultiGetHit<T> (#3611)

Fixes #3554

Author: russcam

src/Nest/Document/Multiple/MultiGet/Response/MultiGetHitJsonConverter.cs

@@ -46,7 +46,12 @@ public override object ReadJson(JsonReader reader, Type objectType, object exist
 			}
 
 			var response = new MultiGetResponse();
+
+			var dateParseHandling = reader.DateParseHandling;
+			reader.DateParseHandling = DateParseHandling.None;
 			var jsonObject = JObject.Load(reader);
+			reader.DateParseHandling = dateParseHandling;
+
 			var docsJarray = (JArray)jsonObject["docs"];
 			if (_request == null || docsJarray == null)
 				return response;

src/Tests/Tests.Reproduce/GithubIssue3554.cs

@@ -0,0 +1,45 @@
+using System.Linq;
+using Elastic.Xunit.XunitPlumbing;
+using FluentAssertions;
+using Nest;
+using Tests.Core.Extensions;
+using Tests.Core.ManagedElasticsearch.Clusters;
+
+namespace Tests.Reproduce
+{
+	public class GithubIssue3554 : IClusterFixture<WritableCluster>
+	{
+		private readonly WritableCluster _cluster;
+
+		public GithubIssue3554(WritableCluster cluster) => _cluster = cluster;
+
+		[I] public void GetManyDoesNotDeserializeDateTimeLikeStringsToDateTime()
+		{
+			var doc = new CreatedAtDocument { CreatedAt = "2009-11-15T14:12:12" };
+			var client = _cluster.Client;
+			var createIndexResponse = client.CreateIndex("githubissue3554", c => c
+				.Mappings(m => m
+					.Map<CreatedAtDocument>(mm => mm
+						.Properties(p => p
+							.Keyword(k => k
+								.Name(n => n.CreatedAt)
+							)
+						)
+					)
+				)
+			);
+
+			createIndexResponse.ShouldBeValid();
+			var indexResponse = client.Index(doc, i => i.Id(1));
+			indexResponse.ShouldBeValid();
+
+			var getManyResponse = client.GetMany<CreatedAtDocument>(new long[] { 1 });
+			getManyResponse.First().Source.CreatedAt.Should().Be(doc.CreatedAt);
+		}
+
+		public class CreatedAtDocument
+		{
+			public string CreatedAt { get; set; }
+		}
+	}
+}