Fix TS Observers type #4756

Job	Run time
ci (ubuntu-20.04, 18, Release)	6m 20s
ci (ubuntu-20.04, 18, Debug)	5m 54s
ci (ubuntu-22.04, 20, Release)	5m 37s
ci (ubuntu-22.04, 20, Debug)	5m 8s
ci (ubuntu-24.04, 20, -Db_sanitize=address, Release)	8m 36s
ci (ubuntu-24.04, 20, -Db_sanitize=address, Debug)	6m 34s
ci (ubuntu-24.04, 20, -Db_sanitize=undefined, Release)	9m 35s
ci (ubuntu-24.04, 20, -Db_sanitize=undefined, Debug)	6m 30s
ci (ubuntu-24.04, 20, -Db_sanitize=thread, Release)	7m 9s
ci (ubuntu-24.04, 20, -Db_sanitize=thread, Debug)	6m 27s
ci (macos-12, 18, Release)	6m 59s
ci (macos-12, 18, Debug)	6m 43s
ci (macos-14, 20, Release)	4m 9s
ci (macos-14, 20, Debug)	3m 58s
ci (windows-2022, 20, Release)	9m 22s
ci (windows-2022, 20, Debug)	8m 41s
	1h 47m 42s

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