[manifest] remove *.spec and add tox.ini

- the ".spec" file was removed by a947cf2aa720
- "tox.ini" was added by ff38b7825e39
3 jobs for topic/default/manifest in 33 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Lint
passed lint_py #118785

00:00:18

 
  Tests
failed pytest #118786

00:00:14

 
  Deploy
skipped install #118787
 
Name Stage Failure
failed
pytest Tests
creating /usr/local/lib/python3.9/site-packages/rdflib_jsonld-0.5.0-py3.9.egg
Extracting rdflib_jsonld-0.5.0-py3.9.egg to /usr/local/lib/python3.9/site-packages
rdflib-jsonld 0.5.0 is already the active version in easy-install.pth

Installed /usr/local/lib/python3.9/site-packages/rdflib_jsonld-0.5.0-py3.9.egg
error: The 'rdflib' distribution was not found and is required by cubicweb
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: command terminated with exit code 1