chore: Fix doctype setup for iframe dev pages

[just-boris]

Description

Without this fix, the doctype inside the iframe is not set. Our components only work with html5 doctype.

Related links, issue #, if available: n/a

How has this been tested?

Locally, by checking document.doctype value

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.04%. Comparing base (680ece3) to head (30a29e4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2783   +/-   ##
=======================================
  Coverage   96.04%   96.04%           
=======================================
  Files         752      752           
  Lines       20979    20979           
  Branches     7147     7138    -9     
=======================================
  Hits        20149    20149           
  Misses        776      776           
  Partials       54       54           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.