Hopefully extremely minor/rare edge case - in game #68631540, both players used Inheritance on Conspirator.
We found that if we played Church, then Estate/Conspirator, it drew a card, despite being the second Action in the turn.
Unsure if this is just an issue facing the Church count, or the Inheritance.
Looks fine to me.
Action 1: Church
Action 2: Estate
Action 3: The set-aside Conspirator
You might be thinking of the original wording of Inheritance, which would have only been two action card plays.
As further explanation to kieranmillar's answer, consider the current text of Inheritance, as established in the October 2019 errata of several cards (you can read what changed and why here: Dominion 2019 Errata and Rules Tweaks (http://forum.dominionstrategy.com/index.php?topic=19893.0))
QuoteInheritance: Event, $7
Once per game: Set aside a non-Command Action card from the Supply costing up to $4. Move your Estate token to it. (During your turns, Estates are also Actions with "Play the card with your Estate token, leaving it there.")
[emphasis mine]
So, you are actually playing the Conspirator card you set aside, and this is the third Action played this turn, after Church and the Estate (which became an Action-Vicory card due to Inheritance).