I researched this for my “Quotes for Entrepreneurs Curate in August 2023” https://www.skmurphy.com/blog/2023/08/31/quotes-for-entrepreneurs-curated-in-august-203/

“I don’t think there is anything I have done that I wish I hadn’t done. Because I learn from everything I do. I’m in school every day. My diploma will be my tombstone.”
Eartha Kitt quoted in “It’s Been a Long Time But…Eartha’s Back!” by Lon Tuck Washington Post Jan-19-1978 https://www.washingtonpost.com/archive/lifestyle/1978/01/19/its-been-a-long-time-but-earthas-back/c17a2e6a-58ad-4b3d-8fef-8f94cbb63d9e/

I think the Playbill quote is derived from this article.