ci: install werkzeug from el8 for Python 3.6

Install werkzeug library in the version distributed in el8, in order to
be as close as this environment as possible and try reproduce #419.

.github/workflows/ci.yml

@@ -56,6 +56,8 @@ jobs:
           pip install PyYAML==5.4.1
           echo "::notice::Installing PyJWT (old version)"
           pip install PyJWT==2.4.0
+          echo "::notice::Installing Werkzeug (old version)"
+          pip install "Werkzeug<0.13"
           echo "::notice::Installing Flask (old version)"
           pip install "flask<2.1.0"
           echo "::notice::Installing requests (old version)"