Your stimulus checks are not "income", according to the tax law. Instead, it's simply an advance payment of a tax credit. And tax credits aren't taxable income.
These two economic impact payments were an advance payment of the Recovery Rebate Credit which is part of the 2020 federal 1040, line 30. Therefore any calculated credit will be reconciled with the payments you received. This refundable credit is for those individuals who did not receive their full amount of their economic impact payments.
If you don't receive a third stimulus check, or receive less than what you're entitled to, you might be able to claim a credit for the amount you're owed on your 2021 tax return.