Run the tools builder on all PRs
Previously, it would only run on changes to subtrees, submodules, or select directories. That made it so that changes to the compiler that broke tools would only be detected on a full bors merge. This makes it so the tools builder runs by default, making it easier to catch breaking changes to clippy (which was the most affected).
r? ``@Mark-Simulacrum`` cc ``@pietroalbini`` ``@flip1995`` ``@m-ou-se``
b2284b9fd1