Set the MD EITC for single childless filers to 28% starting in 2023 (maybe)

The [MD Code](https://casetext.com/statute/code-of-maryland/article-tax-general/title-10-income-tax/subtitle-7-income-tax-credits/section-10-704-effective-until-6302023-for-earned-income) indicates that the match for single childless filers (which is a refundable credit) is 100%. While it specifies that the refundable credit for non-single-childless filers falls to 28% in 2023, it doesn't specify a change for the single childless credit.

[The revised code effective 2023-06-30](https://casetext.com/statute/code-of-maryland/article-tax-general/title-10-income-tax/subtitle-7-income-tax-credits/section-10-704-effective-6302023) also matches the federal EITC at 100% for single childless filers and makes it fully refundable.

Per @ngpsu22, however, [this legislative analysis](https://mgaleg.maryland.gov/2022RS/fnotes/bil_0002/hb0422.pdf) suggests the childless credit also falls from 100% to 28% in 2023:
> In these same tax years, an individual without a qualifying child can claim a refundable credit equal to 100% of the federal credit, subject to a maximum credit of $530. These provisions expire after tax year 2022, and the percentage value of the refundable tax credit for all taxpayers is equal to 28% beginning in tax year 2023.

If we can find a bill that changed it (i.e. the legal code is wrong for some reason), let's change it.