The simplest way would probably be to attempt something that requires admin/elevated privileges (for instance, writing to a registry key/value under HKEY_LOCAL_MACHINE or writing to a file under C:\Program Files) and fail the build if that fails.
Another option would be to call Bill Stewart's isadmin.exe utility (
https://westmesatech.com/?page_id=23) or iselevated (
https://westmesatech.com/?page_id=49) from a Run Program action. Use a 'Success exit codes' field value of 1 to succeed for elevated admins and fail for unelevated admins and non-admins.