End-to-end tests: Print a message if snapshots are changing or not when UPDATE_SNAPSHOTS is set

[madeline-k]

When running the tests with UPDATE_SNAPSHOTS=true, the snapshot files will be automatically updated to match the output of the latest code. Currently, the only way to tell if anything actually changed would be to use git to determine if any files changed after running the tests. It would be helpful to developers to have a message printed showing whether or not something has changed as well.