[faucet] CI fix

Summary: This is the same patch that we needed for other wasm-dependent stuff, we need to include explorer files now that it is in scope

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

Reviewers: #bitcoin_abc, tobias_ruck

Reviewed By: #bitcoin_abc, tobias_ruck

Differential Revision: https://reviews.bitcoinabc.org/D17375