Bug: Liability accounts are included in "Savings Rate" insight card on dashboard

[zachgoll]

Describe the bug A clear and concise description of what the bug is.

On the dashboard, liability accounts like credit cards are being grouped into the "savings rate" insight card, which is always invalid since credit cannot count towards savings.

To Reproduce Steps to reproduce the behavior:

1. Add liability account like a credit card
2. Add an income transaction
3. Go to dashboard
4. See account included in savings rate card

Expected behavior A clear and concise description of what you expected to happen.

We should exclude all liability accounts from the "savings rate" insight card.