Fix spec: should generate default form def from a schema

[jozefizso]

Description

Added key attribute to fieldsets in a default form. This attribute was added in PR #578

Fixes Related issues

• Ensure key is set in fieldsets #578

Checklist

• I have read and understand the CONTRIBUTIONS.md file
• I have searched for and linked related issues
• I have created test cases to ensure quick resolution of the PR is easier
• I am NOT targeting main branch
• I did NOT include the dist folder in my PR

@json-schema-form/angular-schema-form-lead

[Anthropic]

@jozefizso thanks for the PRs, have you taken a look at the webpack/babel branch? Combined with the json-schema-core repo that is the 1.x.x version of the library, I have made a lot of fixes in that already and it could always do with some more people testing it :)