fixup add ability to slim list of unit tests

Author: ianfixes

lib/arduino_ci/ci_config.rb

@@ -231,7 +231,7 @@ def aux_libraries_for_unittest
     # @param paths [Array<String>] the initial set of test files
     # @return [Array<String>] files that match the select/reject criteria
     def allowable_unittest_files(paths)
-      return if @unittest_info[:testfiles].nil?
+      return paths if @unittest_info[:testfiles].nil?
       ret = paths
       unless @unittest_info[:testfiles][:select].nil? || @unittest_info[:testfiles][:select].empty?
         ret = ret.select { |p| unittest_info[:testfiles][:select].any? { |glob| File.fnmatch(glob, File.basename(p)) } }