It's a bad idea...

- commit secret in currently private repo

- 3 years later share / make public

- forget the secret is in the commit history, and still valid, (and relatedly, having long-lived secrets is less secure)

Sure that might not happen for you, but the chances increase dramatically if you make a habit of commiting secrets.

In a large messaging app I worked for we self hosted a gitlab instance for this exact reason. I thought it was over the top but now I get it, you can never be too sure.