Restore use of contextfunction decorator

This code supporting Jinja2<3 was originally using the contextfunction
decorator rather than contextfilter. Although they are both replaced by
pass_context, the old decorators are different.

This resolves the following issue seen in kayobe CI:

    TypeError: handle_repos() missing 1 required positional argument: 'mode'

This was only noticed with kayobe because it uses upper constraints to
install kolla.

Change-Id: Ie4bccb9ed3f4d8782730c5929abbfa73da215a8c

Author: priteau

kolla/template/methods.py

@@ -15,11 +15,11 @@
 import os
 import yaml
 
-# NOTE: jinja2 3.1.0 dropped contextfilter in favour of pass_context.
+# NOTE: jinja2 3.1.0 dropped contextfunction in favour of pass_context.
 try:
     from jinja2 import pass_context
 except ImportError:
-    from jinja2 import contextfilter as pass_context
+    from jinja2 import contextfunction as pass_context
 
 
 def debian_package_install(packages, clean_package_cache=True):