slither-mutate: fix AOR mutator #2222

Job	Run time
tests (ubuntu-latest, unit, 3.8)	52s
tests (ubuntu-latest, unit, 3.12)	51s
tests (ubuntu-latest, integration, 3.8)	3m 9s
tests (ubuntu-latest, integration, 3.12)	3m 11s
tests (ubuntu-latest, tool, 3.8)	55s
tests (ubuntu-latest, tool, 3.12)	49s
tests (windows-2022, unit, 3.8)	1m 33s
tests (windows-2022, unit, 3.12)	1m 30s
tests (windows-2022, integration, 3.8)	3m 56s
tests (windows-2022, integration, 3.12)	2m 33s
tests (windows-2022, tool, 3.8)	2m 22s
tests (windows-2022, tool, 3.12)	3m 58s
coverage	16s
	25m 55s

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