fix: run the suite so its package setup applies

The documented command, discover tests, makes tests/ the top level,
so tests/__init__.py never ran and the variable it sets to keep tests
offline was missing from every local run. Every documented and CI
run now passes -s tests -t ., and a test requires it.

scripts/generate_readme.py

@@ -722,7 +722,7 @@ Full walkthrough: [profiling guide]({link("wiki/profiling")}).
 ## Before opening a PR
 
 ```bash
-python -m unittest discover tests
+python -m unittest discover -s tests -t .
 python scripts/pipeline.py --offline
 ```