## Changes
The full workspace path for a notebook does not contain the notebook's
extension. If a user converts that file path to a relative path (like
`/Workspace/bundle_root/bar/nb` -> `./bar/nb`), they can be confused as
to why the new file path does not work.
The changes in this PR nudge them to add the appropriate file extension
(e.g., `./bar/nb.py` or `./bar/nb.ipynb`).
One common way users can end up in this scenario is by using the view
job as YAML functionality in the Databricks UI.
## Tests
Unit test and manually.
```
(.venv) ➜ bundle-playground git:(master) ✗ cli bundle validate
Error: notebook ./foo not found. Local notebook references are expected
to contain one of the following file extensions: [.py, .r, .scala, .sql, .ipynb]
```