> test: add wait_for_cookie_credentials() to test framework
>
> to be able to ensure the cookie file is written and auth credentials available
> when testing CLI/RPC commands before the RPC connection is up.
> test: fix intermittent race condition in interface_bitcoin_cli.py
>
> by calling wait_for_cookie_credentials() to ensure the cookie file is written
> and auth credentials available for testing the CLI -rpcwait option before the
> RPC connection is up.
This is a backport of Core PR18691