testing: packages/tests/ is not in the helm-unit-tests directory list, so a second chart there would silently never run #3629

Summary

hack/helm-unit-tests.sh walks a hardcoded directory list (packages/apps packages/core packages/extra packages/system packages/library), and packages/tests/ is not in it. The one chart living there today, packages/tests/cozy-lib-tests, runs only because packages/library/cozy-lib's Makefile delegates to it. Any second chart placed under packages/tests/ will silently never run its suites: no failure, no skip notice, nothing. The script's own header says "Keep this list in step with the loop below" and does not mention packages/tests at all, so nothing prompts the next author to add it.

This is the same silent-green class the missing-suite detection work addresses, one level up: there the chart is visited and reports nothing, here the chart is never visited.

Note the fix is not a one-word list addition: visiting packages/tests/ directly would also visit cozy-lib-tests, which is already exercised through the delegation, so the interaction (double run, or dropping the delegation) needs a decision, which is why this is an issue rather than a line in an open PR.

Adjacent cleanup found in the same look

packages/library/testfile is a tracked, empty, purposeless file. It is harmless to this script (the loop skips non-directories), but it is literally the accidental test*-path shape that the shadowed-target check exists to catch, sitting one level above where that check looks. Deleting it is a one-line commit for whoever touches the area.