catch any exception on `singletonclass` #449

Job	Run time
ruby-versions / Generate Ruby versions	4s
test (3.2)	49s
test (3.1)	48s
test (3.0)	44s
test (head)	1m 0s
test (debug)	1m 7s
test (3.4)	1m 0s
test (3.3)	47s
	6m 19s

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