[backport#14453] rpc: Fix wallet unload during walletpassphrase timeout

Summary:
https://github.com/bitcoin/bitcoin/pull/14453/commits/321decffa1fbf213462d97e5372bd0c4eeb99635

and

qa: Ensure wallet unload during walletpassphrase timeout
https://github.com/bitcoin/bitcoin/pull/14453/commits/8907df9e02ec47ef249a7422faa766f06aa01e94

Backport of Core PR14453

Test Plan:

ninja check
./test/functional/test_runner.py wallet_multiwallet

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6249