Use when-let* instead of when-let to support Emacs 30 #481

Job	Run time
build (ubuntu-latest, 27.2, false)	45s
build (ubuntu-latest, 28.2, false)	43s
build (ubuntu-latest, 29.4, false)	1m 6s
build (macos-latest, 28.2, false)	1m 40s
build (macos-latest, 29.4, false)	1m 58s
build (windows-latest, 27.2, false)	1m 38s
build (windows-latest, 28.2, false)	1m 13s
build (windows-latest, 29.4, false)	3m 23s
build (ubuntu-latest, snapshot, true)	33s
build (macos-latest, snapshot, true)	1m 27s
build (windows-latest, snapshot, true)	2m 9s
	16m 35s

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