Rollup merge of #96619 - akiekintveld:same_mutex_check_relaxed_ordering, r=m-ou-se

Relax memory ordering used in SameMutexCheck

`SameMutexCheck` only requires atomicity for `self.addr`, but does not need ordering of other memory accesses in either the success or failure case. Using `Relaxed`, the code still correctly handles the case when two threads race to store an address.