add logging lines to the test runner that indicate config overrides (or lack of)

[ianfixes]

Each of the places in CI where a config file is overridden (or has the opportunity to be overridden), the CI runner script should indicate this to the user.

It should be something like the following cases:

overriding configuration...                                             <none>
overriding configuration...                               test/.arduino-ci.yml
overriding configuration...                          examples/.arduino-ci.yaml
overriding configuration...                 examples/FooSketch/.arduino-ci.yml