[lint] run arc lint on electrum.rs

Summary: Not sure why the linter now wants to reformat this. Doing it in its own diff makes the next commit easier to review

Test Plan: arc lint -- chronik/chronik-http/src/electrum.rs

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18563