fix pyright error in `scipy.cluster` #103

Job	Run time
stubtest-all	59s
lint-and-typecheck	1m 10s
stubtest (scipy.cluster)	44s
stubtest (scipy.constants)	45s
stubtest (scipy.datasets)	47s
stubtest (scipy.fft)	44s
stubtest (scipy.fftpack)	46s
stubtest (scipy.integrate)	44s
stubtest (scipy.io)	45s
stubtest (scipy.linalg)	47s
stubtest (scipy.misc)	47s
stubtest (scipy.odr)	51s
stubtest (scipy.optimize)	44s
stubtest (scipy.special)	45s
stubtest (scipy.stats.contingency scipy.stats.distributions)	48s
stubtest (scipy.version)	41s
	12m 47s

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