chore: Use pull_request_target for changelog preview

[BYK]

Summary

Updates the changelog-preview workflow to use pull_request_target instead of pull_request.

Why?

This change is required for the changelog preview to work correctly with PRs from forks. With pull_request, the workflow runs with a read-only GITHUB_TOKEN which cannot post comments or create statuses on fork PRs.

This aligns with the recommended usage in the craft changelog-preview workflow.

Security Note

This change is safe because the changelog-preview workflow:

• Downloads the Craft binary from releases (not from the PR)
• Only reads git metadata and configuration
• Does not execute any code from the PR

[github-actions]

	Fails
🚫	Please consider adding a changelog entry for the next release.

Instructions and example for changelog

Please add an entry to CHANGELOG.md to the "Unreleased" section. Make sure the entry includes this PR's number.
Example:

## Unreleased

### Fixes/Features

- Use pull_request_target for changelog preview ([#410](https://github.com/getsentry/sentry-cordova/pull/410))

If none of the above apply, you can opt out of this check by adding #skip-changelog to the PR description.

Generated by 🚫 dangerJS against 4520635

[lucas-zimerman]

LGTM!