Bump iframe-resizer from 4.2.3 to 4.2.6 in /arctic/static/arctic

Bumps [iframe-resizer](https://github.com/davidjbradshaw/iframe-resizer) from 4.2.3 to 4.2.6.
- [Release notes](https://github.com/davidjbradshaw/iframe-resizer/releases)
- [Changelog](https://github.com/davidjbradshaw/iframe-resizer/blob/master/CHANGELOG.md)
- [Commits](davidjbradshaw/iframe-resizer@v4.2.3...v4.2.6)

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