[pkg] Fix extra packages not installable For instance `pip install -e ".[pyramid]"` should install the pyramid dependencies. A typo caused all these extra packages to not be found by pip. Closes #16121322.

usr/lib/python2*/*-packages/cubicweb/entities/
usr/lib/python2*/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/python2*/*-packages/cubicweb/*.py