codegen: Fix a nit I commented on #2734. #3

Job	Run time
minimal	9s
rustfmt-clippy	29s
docs	18s
check-cfg	22s
quickchecking	15s
msrv	3m 33s
test-book	8s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	1m 50s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	1m 45s
test-expectations (ubuntu-latest)	1m 6s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	2m 6s
test-expectations (macos-latest)	1m 59s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	1m 50s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	2m 31s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	2m 19s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	2m 24s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	2m 15s
test (ubuntu-latest, 16.0, 1, 0, 0, 0, 0)	2m 37s
test (ubuntu-latest, 16.0, 1, 0, 0, 1, 0)	2m 38s
test (ubuntu-latest, 16.0, 1, 0, 1, 0, 0)	3m 10s
test (ubuntu-latest, 16.0, 1, 0, 1, 1, 0)	3m 1s
test (ubuntu-latest, 16.0, 1, 1, 0, 0, 0)	3m 33s
test (ubuntu-latest, 16.0, 1, 1, 0, 1, 0)	3m 8s
test (ubuntu-latest, 16.0, 1, 1, 1, 0, 0)	3m 0s
test (ubuntu-latest, 16.0, 1, 1, 1, 1, 0)	3m 12s
test (ubuntu-latest, 16.0, 0, 0, 1)	1m 46s
test (macos-latest, 9.0, 0, 0, 0)	1m 33s
	52m 57s

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