Add interface-forge to Testing Frameworks

[Goldziher]

Checklist:

• I've read and understood Contributing Guidelines.
• I've added the new resource at the end of its section.
• This resource is out there for a while, and actively maintained. — first released 2021, still actively maintained
• This resource is popular enough and has at least a few hundred stars on GitHub. — 102★, so short of a few hundred. Flagging it honestly rather than checking the box; happy for you to close if that's the bar.

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interface-forge is type-safe mock and fixture data generation for TypeScript, built on factories with Faker integration.

On the placement note: it was previously dropped directly under ## Testing Frameworks with no subsection, which was wrong. It's now at the end of ### Assertion, which is where the existing stubbing and mocking entries live (Sinon.JS, proxyquire, Pocket Mocker). Happy to move it elsewhere if you'd rather it sat somewhere else.

[gokaygurcan]

Wrong placement. Plus, respect the PR template.

[Goldziher]

Thanks @gokaygurcan — both points addressed.

Placement: it was sitting directly under ## Testing Frameworks outside any subsection. It's now at the end of ### Assertion, next to the other stubbing/mocking entries (Sinon.JS, proxyquire, Pocket Mocker). Let me know if you'd prefer it somewhere else.

Template: checklist filled in. I've left the stars box unchecked — it's at 102★, which is short of "a few hundred," so that's your call rather than mine to tick.