"Under a California law that took effect on January 1, 2020, employers will have to provide extra notices to California employees enrolled in flexible spending accounts (FSAs) explaining the 'use it or lose it' federal tax rules that apply to those FSAs.... [Although the language] could be read to apply only to mid-year deadlines to withdraw funds, such as in the case of termination of employment, the limited legislative history suggests that the author was actually concerned more generally with funds remaining in an account at year-end being forfeited."