Arrow marker on `<details>` element doesn't update

[AtkinsSJ]

Noticed this on the WPT tests that have subtests. They use <details> to view the assertions that were made for each subtest.

Test case: Open this, and then open and close the details element.

<details>
  <summary>Summary</summary>
  Some details go here.
</details>

The arrow should change, and it used to do so, but now it doesn't. My guesses are that either this is a failure to invalidate the style, or I messed something up with my recent pseudo-element changes. 😅 I haven't had time to check.

[AtkinsSJ]

Pinging @kalenikaliaksandr - I bisected this to 9b26f7eb0faaca63ee9109c6eda44c82a6acfeaf