Remove invulnerability from Pugna before dialog explains that you can stun him

[Shushishtok]

ABILITY USE: "Stun Pugna" section has a pause where you are told your hero will walk to the enemy and use it when they're close enough, but this comes before Pugna is targettable so it creates a moment.

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Currently, Pugna Purge can only be stunned after the dialog ends, due to him being invulnerable, which causes confusion. Allow players to stun them while the dialog is still going.

[Shushishtok]

I originally fixed it, but then reverted it. It doesn't make much sense to stun and kill Purge before he even had a chance to annoy you. Need to rethink this.