Fix small copy-paste error (dotnet#7701)

Author: kant2002

xml/System.Runtime.InteropServices/Marshal.xml

@@ -2473,7 +2473,7 @@
  <format type="text/markdown"><![CDATA[
 
 ## Remarks
- You can use <xref:System.Runtime.InteropServices.Marshal.FreeCoTaskMem%2A> to free any memory allocated by <xref:System.Runtime.InteropServices.Marshal.AllocCoTaskMem%2A>, <xref:System.Runtime.InteropServices.Marshal.ReAllocCoTaskMem%2A>, or any equivalent unmanaged method. If the `ptr` parameter is `null`, the method does nothing.
+ You can use <xref:System.Runtime.InteropServices.Marshal.FreeCoTaskMem%2A> to free any memory allocated by <xref:System.Runtime.InteropServices.Marshal.AllocCoTaskMem%2A>, <xref:System.Runtime.InteropServices.Marshal.ReAllocCoTaskMem%2A>, or any equivalent unmanaged method. If the `ptr` parameter is `IntPtr.Zero`, the method does nothing.
 
  <xref:System.Runtime.InteropServices.Marshal.FreeCoTaskMem%2A> exposes the COM [CoTaskMemFree](https://go.microsoft.com/fwlink/?LinkId=148638) function, which frees all bytes so that you can no longer use the memory that the `ptr` parameter points to.