net: clarify the behavior of UCred::pid() on Cygwin
          #7611
        
          
      
                
     Merged
            
            
          
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Motivation
#7393 added support for Cygwin but it didn't update the documentation of tokio::net::ucred::UCred::pid() to mention that
Solution
Add
Cygwinto the list of supported OSes for tokio::net::ucred::UCred::pid()