Set errno on NotWritableError (conda#9789)

The  `NotWritableError` exception does accept the `errno` argument, but does not pass it to `OSError` (its 2nd parent class). This causes the `errno` attribute to be unset (defaults to `None`).

Co-authored-by: Michael C. Grant <[email protected]>

conda/exceptions.py

@@ -892,6 +892,7 @@ def __init__(self, path, errno, **kwargs):
                 'gid': os.getegid(),
             })
         super(NotWritableError, self).__init__(message, **kwargs)
+        self.errno = errno
 
 
 class NoWritableEnvsDirError(CondaError):