hdl._nir: AssignmentList: fix comb_edges_to #3565

Job	Run time
document	52s
smoke (amaranth-lang/amaranth-boards)	29s
check-links	49s
smoke (amaranth-lang/amaranth-stdio)	43s
smoke (amaranth-lang/amaranth-soc)	41s
test (3.8)	2m 27s
test (3.9)	2m 33s
test (3.10)	2m 14s
test (3.11)	2m 40s
test (3.12)	3m 28s
test (pypy-3.8)	5m 20s
test (pypy-3.9)	4m 45s
test (pypy-3.10)	4m 52s
test (3.13-dev)	3m 3s
publish-docs	6s
publish-docs-dev	0s
required	1s
publish-schemas	5s
publish-package	38s
publish-release	0s
	35m 46s

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