[Update Request]: Microsoft.Sysinternals.RDCMan 3.21

### What type of update are you requesting?

A new version of an existing package

### Current Package Identifier

Microsoft.Sysinternals.RDCMan

### Package Version

3.12 => 3.21

### Please describe the changes you would like to see

There is a new release (3.21) available.
Download Page Url: https://learn.microsoft.com/en-us/sysinternals/downloads/rdcman

Locate the manifest for Microsoft.Sysinternals.RDCMan in the winget-pkgs repository and compare its current 3.12 metadata with the 3.21 release on the linked download page. Update the package metadata for the new release and validate the manifest using the repository's standard checks; done means the 3.21 package is accepted without validation errors.

Written by the indexing model from the issue text.