Apply simple rubocop fixes

test/unit/strainer_unit_test.rb

@@ -36,7 +36,8 @@ class StrainerUnitTest < Minitest::Test
     rescue Liquid::ArgumentError => e
       assert_match(
         /\ALiquid error: wrong number of arguments \((1 for 0|given 1, expected 0)\)\z/,
-        e.message)
+        e.message
+      )
       assert_equal e.backtrace[0].split(':')[0], __FILE__
     end
   end
@@ -135,7 +136,7 @@ class StrainerUnitTest < Minitest::Test
   end
 
   module LateAddedFilter
-    def late_added_filter(input)
+    def late_added_filter(_input)
       "filtered"
     end
   end
@@ -150,7 +151,7 @@ class StrainerUnitTest < Minitest::Test
     mod = Module.new do
       class << self
         attr_accessor :include_count
-        def included(mod)
+        def included(_mod)
           self.include_count += 1
         end
       end