test `show_templates.py` will fail for datasets that require manual download

this test (mostly for checking/render and print templates) is bound to fail for datasets that require manual download.
to do: handle these cases by returning a warning for instance? not even sure it's possible

Start with the test in show_templates.py, especially the checks for rendering and printing templates, and reproduce the failure with a dataset that requires manual download. Trace how that dataset is detected or loaded, then define and test the expected warning behavior for cases the test cannot download automatically.

Written by the indexing model from the issue text.