Some of the test cases access fields of the backend that are supposed to be
locked while the test is running, which can trigger the race detector. I fixed
a few of these in #17411, but I missed these two cases.
Updates #15160
Updates #17192
Change-Id: I45664d5e34320ecdccd2844e0f8b228145aaf603
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>