test: add a test case for StyleSheet mutation exceptions while fast-forwarding #887
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This PR is related to a bug that @Juice10 and I found at the last core team meeting.

The added test case can reproduce the problem but I haven't found a solution yet. So that the CI will absolutely fail and it is expected.
The reason for this bug is similar to PR #865. When childNodes of a style element are mutated (append or remove), all applied stylesheet rules programmatically are lost automatically.