Fixed flake8 session until flake8-bandit works with latest bandit 1.7.3

Author: Sylvain MARIE

ci_tools/flake8-requirements.txt

@@ -2,6 +2,7 @@ setuptools_scm>=3,<4
 flake8>=3.6,<4
 flake8-html>=0.4,<1
 flake8-bandit>=2.1.1,<3
+bandit<1.7.3
 flake8-bugbear>=20.1.0,<21.0.0
 flake8-docstrings>=1.5,<2
 flake8-print>=3.1.1,<4