Add option to fail docs build on gallery example execution error (#256)

# References and relevant issues
Closes napari/napari#6392
Depends on #255

# Description
Added a sphinx gallery option to fail the docs build on example
execution failure.

Right now, this _should_ fail on CI due to one of our example failing,
but the docs build will anyway depend on the #255.

Co-authored-by: Peter Sobolewski <[email protected]>

Author: melissawm

docs/conf.py

@@ -254,7 +254,8 @@ def napari_scraper(block, block_vars, gallery_conf):
     'plot_gallery': "'True'",  # https://github.com/sphinx-gallery/sphinx-gallery/pull/304/files
     'download_all_examples': False,
     'min_reported_time': 10,
-    'only_warn_on_example_error': True,
+    'only_warn_on_example_error': False,
+    'abort_on_example_error': True,
     'image_scrapers': ("matplotlib", napari_scraper,),
     'reset_modules': (reset_napari,),
     'reference_url': {'napari': None},