chore: run tests on main

[dkarter]

Motivation

Run CI for the branch this repository actually uses. The repo does not use master, so pull request checks need to target main.

Summary of Changes

• Changes the test workflow push trigger from master to main.
• Changes the pull request trigger from master to main.
• Leaves the existing exact-pinned action versions unchanged.

Testing

• mise run fmt:check

Dependencies/Special Considerations

Linear: RMS-77

This PR should be the root of the active implementation stack.

Stack

1. chore: run tests on main #8 👈 current
2. feat: add neovim lua plugin scaffold #6
3. feat: continue standard bullets #4
4. feat: support ordered bullet continuations #7