Fix M24 parameter description (dotnet#5193)

Author: gewarren

xml/System.Numerics/Matrix4x4.xml

@@ -163,7 +163,7 @@
         <param name="m21">The value to assign to the first element in the second row.</param>
         <param name="m22">The value to assign to the second element in the second row.</param>
         <param name="m23">The value to assign to the third element in the second row.</param>
-        <param name="m24">The value to assign to the third element in the second row.</param>
+        <param name="m24">The value to assign to the fourth element in the second row.</param>
         <param name="m31">The value to assign to the first element in the third row.</param>
         <param name="m32">The value to assign to the second element in the third row.</param>
         <param name="m33">The value to assign to the third element in the third row.</param>