I do not know yet what's causing this flake, but I've debugged it enough
to be confident that it's not a serious issue; it seems to be a test
flake. There is some path through which the tree nodes or keys might
still be transiently reachable, but I don't yet know what that is.
Details about what I tried and ruled out are in the code.
For #74083.
Change-Id: I97cdaf3f97e8c543fcc2ccde8b7e682893ae2f97
Reviewed-on: https://go-review.googlesource.com/c/go/+/697341
Auto-Submit: Michael Knyszek <mknyszek@google.com> Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>