[API] Test Runner: Use strict_encode for base 64 variables

Author: picandocodigo

api-spec-testing/test_file/task_group.rb

@@ -304,7 +304,7 @@ def transform_and_set_variable(action)
                   fields.include?(key)
                 end.values if fields
 
-                to_set = Base64.encode64(values_to_encode.join(':'))
+                to_set = Base64.strict_encode64(values_to_encode.join(':'))
                 @test.cache_value(response_key, to_set)
               end
             end