Fix jinja2>=2.9 nested include vars (#35099)

This fixes a bug when parent's local vars where not available in nested
includes. The bug can only be seen with jinja>=2.9 which changes
how the variable scopes work.

Fixes #34886

test/integration/targets/template/templates/for_loop_include.j2

@@ -0,0 +1,3 @@
+{% if par_var is defined %}
+{% include 'for_loop_include_nested.j2' %}
+{% endif %}