* other: master -> main
I'm so used to using `main` branch now that it's actually kinda annoying
to use `master` for just this repo... so might as well rename it now.
* overzealous change
* wording
* some wording
* allow auto-cancel for tests if not main
* docs: bump mkdocs-related dependencies to latest
bumps mkdocs-material to 9.4.8, mkdocs to 1.5.3, mkdocs-material-extensions to 1.3
* fix some link warnings