This commit picks up etcd-io/etcd#12790, which
resolves a regression observed in cockroachdb#62212.

Picks up the following four commits:
- etcd-io/etcd@87258ef
- etcd-io/etcd@2c2456b
- etcd-io/etcd@ebc0174
- etcd-io/etcd@e51c697

```
name                  old time/op    new time/op    delta
EntryCache-16            114µs ± 7%      96µs ±12%  -15.29%  (p=0.000 n=19+19)
EntryCacheClearTo-16    37.7µs ± 4%    34.9µs ± 4%   -7.55%  (p=0.000 n=17+18)

name                  old alloc/op   new alloc/op   delta
EntryCacheClearTo-16    1.28kB ± 0%    0.77kB ± 0%  -40.00%  (p=0.000 n=20+20)
EntryCache-16           83.3kB ± 0%    50.0kB ± 0%  -39.95%  (p=0.000 n=19+20)

name                  old allocs/op  new allocs/op  delta
EntryCache-16             3.00 ± 0%      3.00 ± 0%     ~     (all equal)
EntryCacheClearTo-16      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
```