.gitlab-ci.yml: execute flake8 in tests jobs

.gitlab-ci.yml

@@ -21,9 +21,11 @@ tests:
     - pip install lazyparser==0.2.0
     - pip install pyfaidx==0.5.7
     - pip install biopython==1.75
+    - pip install flake8
   script:
     - coverage run -m unittest discover
     - coverage xml
+    - flake8 --output-file .flake8-report.txt
   artifacts:
     untracked: true