Run tests against TypeScript 7

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the issue has not already been raised

Issue

In #16503 we found our first TypeScript-7-specific bug, so it's about time we ran tests against both TypeScript 5 and TypeScript 7. This bug was also skipLibCheck specific, so we likely need a testing matrix of TypeScript versions, exactOptionalProperties true/false, skipLibCheck true/false, and strict true/false.