fix: correctly serialize object assignment expressions

[dummdidumm]

fixes #12174
#12109 didn't take into account actual object assignments and couldn't differentiate them from our "fake" assignments, this fixes that

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[changeset-bot]

🦋 Changeset detected

Latest commit: 07662d4

The changes in this PR will be included in the next version bump.

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svelte	Patch

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