Test against jinja2 3.0

New installs of the 2.x branch are currently broken due to https://github.com/pallets/jinja/issues/1585, which the maintainer of jinja apparently does not intend to fix.

(jinja2 3.1 drops compatibility shims for 2.x, which we don't want to do in an LTS backport)

setup.py

@@ -45,7 +45,7 @@ testing_extras = [
     'python-dateutil>=2.7',
     'pytz>=2014.7',
     'elasticsearch>=5.0,<6.0',
-    'Jinja2>=2.11,<3.0',
+    'Jinja2>=3.0,<3.1',
     'boto3>=1.16,<1.17',
     'freezegun>=0.3.8',
     'openpyxl>=2.6.4',