rename master branch references to main

[paulirish]

I already made the branch name change here, as of 5 minutes ago. If you have a local git checkout of this repo... run the following before your next pull:

git branch -m master main; git fetch origin; git branch -u origin/main main; git remote set-head origin -a

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of the changes:

• 1 of these is LH repo. ref core: finalize master => main branch rename lighthouse#14409
• a few are the chrome-launcher repo
• and then a few are chromium repo

[brendankenny]

👍