Update ConversionExamples.cs (#46796)

Author: fcdeveloper00

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

@@ -17,7 +17,7 @@ private static void CastExampleQuery()
         // <CastOperatorQuerySyntax>
         IEnumerable people = students;
 
-        var query = from Student student in students
+        var query = from Student student in people
                     where student.Year == GradeLevel.ThirdYear
                     select student;