Fix: aleph account balance miss await

[1yam]

aleph account balance missed a await on response.json()

[github-actions[bot]]

• The changes are limited to a single file: src/aleph_client/commands/account.py.
• The modification involves updating the way response data is handled in an async function, specifically changing from synchronous response.json() to asynchronous await response.json(). This is a minor change that doesn't introduce any new features or modify existing logic in a significant way.
• There are no indications of extensive changes or system-level knowledge required for this PR.