PSAvoidAssignmentToAutomaticVariable Errors on validateset

I have been getting errors on validateset because PSScriptAnalyzer is confusing the validateset as assignment.

An example of this happening is

[validateset($True, $False)]
[bool]$UnfurlLinks,

[validateset($True, $False)]
[bool]$UnfurlMedia,

from https://github.com/RamblingCookieMonster/PSSlack/blob/master/PSSlack/Public/New-SlackMessage.ps1