Fix CamelCaseKeys type

[nano72mkn]

The type of camelCaseKeys is incorrect and has been fixed.
When the type is object or undefined, the hierarchy after that remains in snakeCase.

interface ObjectOrUndefined {
	foo_bar: {
		foo_bar: {
			foo_bar: boolean;
		} | undefined;
	};
}

const objectOrUndefined: ObjectOrUndefined = {
	foo_bar: {
		foo_bar: {
			foo_bar: true
		}
	}
};

expectType<{ fooBar: { fooBar: { fooBar: boolean } | undefined } }>(
	camelcaseKeys(objectOrUndefined, {deep: true})
);

As a result of the test, the following error occurred.

Argument of type { fooBar: { fooBar: { foo_bar: boolean; } | undefined; }; } is not assignable to parameter of type { fooBar: { fooBar: { fooBar: boolean; } | undefined; }; }.
  The types of fooBar.fooBar are incompatible between these types.
    Type { foo_bar: boolean; } | undefined is not assignable to type { fooBar: boolean; } | undefined.
      Property fooBar is missing in type { foo_bar: boolean; } but required in type { fooBar: boolean; }. 

With this fix, the conversion will be correct as follows

{ fooBar: { fooBar: { fooBar: boolean } | undefined } }

[sindresorhus]

Tests are failing.

[sindresorhus]

@g-plane Would you be able to help review?

[g-plane]

I think the failing tests aren't introduced in this PR, because the commits on main branch also break the tests.