It isn't voluntary if the date and time is chosen for you. California allows the employer to choose the last day of work. Not the effective date of resignation.

"An involuntary leaving of work occurs when the employer is the moving party in causing the unemployment of an employee at a time when the employee is able and willing to continue working."[1]

Gebru said she would respond after she was back from vacation.[2] So she was willing to continue working that long at least.

[1] http://carules.elaws.us/code/t.22_d.1_subd.1_d.1_pt1_ch.5_ar...

[2] https://twitter.com/timnitgebru/status/1334341991795142667