Typo in addEventListener - use evt instead of event

[JacobMonticello]

Description

In addEventListener, when the triggerSpec.changed if block was entered, node was being set to event.target. This technically works, but is deprecated and should use evt.target instead like the rest of addEventListener.

Corresponding issue: #3179

Testing

Smoke test a basic changed trigger flow. /hello should get called as expected (meaning that node, and thus node.value are still getting assigned as expected):

<select id="select">
  <option>1</option>
  <option>2</option>
</select>

<div hx-get="/hello" hx-trigger="click changed from:#select"></div>

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded