Fix tests for changes in @types/unist

Author: wooorm

test.js

@@ -16,7 +16,9 @@ test('unist-util-size', function (t) {
 
   t.equal(size(tree), 11, 'complete tree')
   t.equal(size(tree.children[0]), 7, 'parent node with mixed children')
+  // @ts-expect-error: fine.
   t.equal(size(tree.children[0].children[1]), 1, 'parent of text')
+  // @ts-expect-error: fine.
   t.equal(size(tree.children[0].children[0]), 0, 'text node')
 
   t.equal(size(tree, 'element'), 5, 'test')