Follow-up for #2929932: two @todos left for that issue that actually already have been addressed

Problem/Motivation

See #2929932-40: Work around core's ill-designed @FieldType-level TimestampItemNormalizer normalization until #2926508 lands:

1. +++ b/tests/src/Functional/FeedTest.php
   @@ -127,18 +124,14 @@ class FeedTest extends ResourceTestBase {
   -          'modified' => 123456789,
   +          'modified' => '1973-11-29T21:33:09+00:00',
              // @todo uncomment this in https://www.drupal.org/project/jsonapi/issues/2929932
              /* 'modified' => $this->formatExpectedTimestampItemValues(123456789), */
   

   Rather than updating the existing entry, I should've uncommented the todo.

2. +++ b/tests/src/Functional/NodeTest.php
   --- a/tests/src/Functional/ResourceTestBase.php
   +++ b/tests/src/Functional/ResourceTestBase.php
   

   There was a big todo in this class, which I forgot to address.

Creating a follow-up…

Proposed resolution

Address those.

Remaining tasks

N/A

User interface changes

None.

API changes

None.

Data model changes

None.