[Backport 7.x] Support deserialisation of simple scripts

src/Nest/CommonOptions/Scripting/ScriptFormatter.cs

@@ -23,6 +23,12 @@ internal class ScriptFormatter : IJsonFormatter<IScript>
 
 		public IScript Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver)
 		{
+			if (reader.GetCurrentJsonToken() == JsonToken.String)
+			{
+				var scriptValue = reader.ReadString();
+				return new InlineScript(scriptValue);
+			}
+
 			if (reader.GetCurrentJsonToken() != JsonToken.BeginObject)
 			{
 				reader.ReadNextBlock();

tests/Tests.Reproduce/GitHubIssue5684.cs

@@ -0,0 +1,35 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System.Text;
+using Nest;
+using System.Runtime.Serialization;
+using System.IO;
+using FluentAssertions;
+using Elastic.Elasticsearch.Xunit.XunitPlumbing;
+
+namespace Tests.Reproduce
+{	
+	public class GitHubIssue5684
+	{
+		private static readonly byte[] ResponseBytes = Encoding.UTF8.GetBytes(@"{
+    ""script"": ""doc['sales_price'].value * 2""
+}");
+
+		[U]
+		public void DeserialiseSimpleScript()
+		{
+			var client = new ElasticClient();
+			var result = client.RequestResponseSerializer.Deserialize<Sample>(new MemoryStream(ResponseBytes));
+			result.Should().NotBeNull();
+			result.Script.Should().BeOfType<InlineScript>().Subject.Source.Should().Be("doc['sales_price'].value * 2");
+		}
+
+		private class Sample
+		{
+			[DataMember(Name = "script")]
+			public IScript Script { get;set; }
+		}
+	}
+}