Deprecated usage liquid Template.file_system

[adangel]

We seem to use a deprecated feature of liquid:

[DEPRECATION] Template.file_system= is deprecated. Use Environment#file_system= instead. Called from /home/runner/work/pmd-regression-tester/pmd-regression-tester/lib/pmdtester/builders/liquid_renderer.rb:15:in `render_liquid'

pmd-regression-tester/lib/pmdtester/builders/liquid_renderer.rb

Line 15 in 2f41252

Liquid::Template.file_system = includes

https://github.com/Shopify/liquid/blob/cbd8a0a2ee2cd3f12516c52558e5a894d1fd792a/lib/liquid/template.rb#L47-L50

We should probably use

Liquid::Environment.default.file_system = includes