Also show `default-branch-button` on Commit lists #2936

It appears here: https://github.com/sindresorhus/refined-github/tree/6c46766237ccbf8a8c23ba07aca1e48a11a71b4b <img width="305" alt="code" src="https://user-images.githubusercontent.com/1402241/77597670-e40d1580-6eff-11ea-83e7-a0b3f60b7042.png">

But not on isCommitList: https://github.com/sindresorhus/refined-github/commits/6c46766237ccbf8a8c23ba07aca1e48a11a71b4b

<img width="457" alt="commits" src="https://user-images.githubusercontent.com/1402241/77597683-ea02f680-6eff-11ea-9f49-d8c5e5351ca0.png">