fix: make sure to break formData reactivity

[MaxPostema]

Checklist

• [x] Functionality works & meets specifications
• [x] Code reviewed
• [ ] Code unit/integration/system tested
• [x] User documentation updated
• [x] Clean commits
• [x] No warnings during install
• [x] Updated flow typing
• [ ] Add fix/feature to molgenis-frontend release draft
• [ ] Update package version in molgenis-frontend release draft

[molgenis-jenkins]

:tada: This PR is included in version 5.9.3 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: