Auto merge of #17935 - cbrewster:ce_upgrades, r=jdm

Custom element upgrades

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17935)
<!-- Reviewable:end -->

tests/wpt/mozilla/meta/MANIFEST.json

@@ -26534,7 +26534,7 @@
    "testharness"
   ],
   "mozilla/collections.html": [
-   "f1029d519aa7017a1a3d18a891a0774b9a39f847",
+   "aa060d1e5d1364224f2c2151e5f8b9580ac4427e",
    "testharness"
   ],
   "mozilla/createEvent-storageevent.html": [
@@ -27534,7 +27534,7 @@
    "testharness"
   ],
   "mozilla/prototypes.html": [
-   "bb4824ae242ed89485a272f6ef74631d6fea62be",
+   "e19d75682a83f4d2de1cbdf053aadfda181d6725",
    "testharness"
   ],
   "mozilla/proxy_setter.html": [