[cashtab-faucet] Patch bug in Dockerfile

Summary: ecash-wallet files are not copied in the wasm stage like the ecash-lib files. Need to do this before running npm ci

Test Plan: docker build -f cashtab-faucet.Dockerfile -t cashtab-faucet_local .

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18389