There is some imprecision probably in the internal HTTPRPCTimer class
(haven't exactly figured out where).
But we can't expect that waiting exactly 2 seconds right after calling
walletpassphrase(2) will result in a locked wallet due to the nature how
we internally handle threads/timers.

The wallet_encryption test fails regularly in CIs.

for i in {1..100}
do
  ./test/functional/test_runner.py wallet_encryption
done