Using with-utf8 so we don't encounter weird locale issues anymore

[msooseth]

Description

Uses with-utf8 to fix potential (future) issues with locale in cli.hs. All our tests etc. run in nix-shell so they are fine, no need to complicate them. However, the cli actually gets released as a static binary, we should make sure we don't accidentally have/introduce locale issues

Checklist

• [x] tested locally
• [ ] added automated tests
• [ ] updated the docs
• [x] updated the changelog