test

Fix an error when `str.length` is greater than `length` #518

Job	Run time
steep-check (head)	26s
test-memory (head)	33s
test-ruby (head, master)	6m 5s
check-misc (head)	15s
test-ruby (3.0, master)	5m 49s
test-windows (head)	1m 42s
ruby-versions / Generate Ruby versions	3s
test-cpp (head, g++)	14s
test (2.5)	30s
test-cpp (head, clang++)	28s
test (2.6)	39s
test (2.7)	32s
test (3.0)	13s
test (3.1)	17s
test (3.2)	14s
test (3.3)	14s
test (head)	16s
	18m 30s

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