Update C# linq-related snippet 'GroupQueryResults.cs' (#46817)

Hi, First of all, thanks a lot for your efforts and your rich contents.
In the first lines of 'GroupByPropertyMethod' method, which is  commented lines, the query variable name should be changed to GroupByYearQuery , and also the type of it to
IEnumerable<IGrouping<GradeLevel,DataClass.Student>>.

Author: fcdeveloper00

docs/csharp/linq/standard-query-operators/snippets/standard-query-operators/GroupQueryResults.cs

@@ -51,7 +51,7 @@ orderby newGroup.Key
     public static void GroupByPropertyMethod()
     {
         // <GroupByPropertyMethod>
-        // Variable groupByLastNamesQuery is an IEnumerable<IGrouping<string,
+        // Variable groupByYearQuery is an IEnumerable<IGrouping<GradeLevel,
         // DataClass.Student>>.
         var groupByYearQuery = students
             .GroupBy(student => student.Year)