[chore] Fix codecov

[lestrrat]

After we shuffled around the branches, codecov isn't working as expected.
I'm sure this is something silly, but I personally am not that into the code coverage game and don't feel like spending time on it. It would be nice if someone knowledgeable can give me a hand.

[thomasrockhu-codecov]

@lestrrat, Tom from Codecov here. I noticed two things

1. The Codecov GitHub app needs to be installed
2. The default branch (develop/v2?) is not being set here

[lestrrat]

OMG, I didn't expect somebody from codecov to jump in so fast! (egosurfing much? :)
Thank you very much, and let me check your suggestions

[thomasrockhu-codecov]

Ha! Something something slack integration 🤷‍♂️. Let me know if that doesn't work for you!