Rename primary branch to main

[mhdawson]

We are going through all of the node.js repositories to rename the primary branch to main. Please see nodejs/node#33864 for more context.

There are some references to the master branch in the files so I think I'll need some help in doing the update. @richardlau is that something you can help with?

[richardlau]

@mhdawson I can do this.

[nschonni]

I opened up nodejs/build#2831 for the hook

[mhdawson]

@richardlau, @nschonni I think in addition to nodejs/build#2831 along with the default branch rename, we would need to log into the machine the webhook and scripts are deployed to and update the files there manually as well. Is there anything else you think we need to do?

Looking at the repo itself the only references to master seen to be in external repos: https://github.com/nodejs/unofficial-builds/search?q=master so I don't think those need to be updated.