Mark some ResizeObserver tests as flaky

[mrobinson]

ResizeObserver isn't completed.

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes do not require tests because this just updates test expectations.

[gterzian]

thanks for noticing, I've added notes about these in #31182.

The relevant notes are:

• iframe-same-origin.html appears intermittent for an unknown reason(I haven't seen it fail locally yet, making it hard to debug so far). See Mark some ResizeObserver tests as flaky #32546
• observe.html At least one test(test7?) appears intermittently to timeout, and when it passes it makes other test fails(as opposed to not run). See Fix DOMRect calc in ResizeObserverEntry #32549 for how to make at least three tests pass. Others remain to un-investigated.

[mrobinson]

Thanks for the review!