CI/CD: test only the packages and crates a pull request touches

Add pull_requests: { tests: touched } to the production branch's runtime.yml. A pull request into the production branch then runs only the tests of the packages (nearest package.json) and crates (nearest Cargo.toml) that hold its changed files, plus steps whose inputs it changes and steps that read every file. The other tests its change reaches are listed on the left to main job, and the production branch's check runs them after the merge. Turn on undo with it so that a commit that breaks the production branch is reverted automatically. A change to a root file other than Markdown, a file in a dot folder, a lockfile or toolchain file, a script a step runs, or the config file runs every test it reaches. The default, tests: reached, is unchanged.