Description

The typescript type claims that the event parameter for HtmxExtension.onEvent can take Event|CustomEvent, but that's not true it can only ever receive a CustomEvent. Fix this since it's not a requirement for extensions to deal with an Event and the definition of that type doesn't have a detail property.

Testing

Ran npm run types-check, the dist script and npm run types-generate to verify the type is now correct.

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