ci/github-script: default to commonjs

Since all github-scripts need to be written in commonjs, we now default
to it by not setting package.json. Support from editors for .js files is
slightly better than .cjs. To still allow using module imports in the
test runner script, we trick node into loading the script itself as a
module again via `--import ./run`.

ci/github-script/.editorconfig

@@ -1,4 +1,3 @@
-# TODO: Move to <top-level>/.editorconfig, once ci/.editorconfig has made its way through staging.
-[*.cjs]
+[run]
 indent_style = space
 indent_size = 2