hdl._nir: AssignmentList: fix comb_edges_to #3559

Job	Run time
check-links	44s
document	43s
smoke (amaranth-lang/amaranth-boards)	30s
test (3.8)	2m 40s
smoke (amaranth-lang/amaranth-stdio)	41s
test (3.9)	2m 14s
smoke (amaranth-lang/amaranth-soc)	40s
test (3.10)	2m 19s
test (3.11)	2m 40s
test (3.12)	3m 37s
test (pypy-3.8)	5m 12s
test (pypy-3.9)	4m 50s
test (pypy-3.10)	4m 58s
test (3.13-dev)	2m 59s
publish-docs	4s
publish-docs-dev	0s
required	1s
publish-package	41s
publish-schemas	5s
publish-release	0s
	35m 38s

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