Update libprio-rs: Prio3Sum w/ `max_measurement` rather than `bits`. #8936

Job	Run time
janus_interop_docker	9m 55s
janus_lints (stable minus 2 releases)	6m 48s
janus_docker	15m 18s
janus_lints (stable)	6m 14s
rustsec_advisories	29s
janus_build (stable minus 2 releases)	14m 46s
janus_build (stable)	14m 33s
	1h 8m 3s

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