Merge pull request #11979 from edx/robrap/linter

TNL-4214/TNL-4287: Enhance safe template linter

scripts/tests/templates/includes/include_safe.html

+## Mako template with safe by default page expression
+<%page expression_filter="h"/>

scripts/tests/templates/includes/include_unsafe.html

+## Mako template with no safe by default page expression

scripts/tests/templates/test.html

+<%include file="./includes/include_safe.html" args="message" />
+
+<%include file="./includes/include_unsafe.html" args="message" />
+
+<%include file="bad_file_name.html" />
+
+## safe-lint: disable=mako-include-with-violations
+<%include file="bad_file_name.html" />