[#61546] Fix DangerDialog scroll behaviour w/form + system test

[myabc]

⚠️ This PR is based on #243 - please review/merge that PR first.
⚠️ This PR requires an upstream enhancement to Cuprite in order for tests to run green - rubycdp/cuprite#291

What are you trying to accomplish?

Fix Danger Dialog scroll behaviour when the dialog contains a form + verify behaviour is correct with system test.

Screenshots

See #243

Integration

N/A

List the issues that this change affects.

https://community.openproject.org/wp/61546

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

What approach did you choose and why?

Anything you want to highlight for special attention from reviewers?

Accessibility

• Fixes axe scan violation - This change fixes an existing axe scan violation.
• No new axe scan violation - This change does not introduce any new axe scan violations.
• New axe violation - This change introduces a new axe scan violation. Please describe why the violation cannot be resolved below.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Lookbook)
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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Latest commit: 83fd601

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