Provide default for retrieve_files method

Fixes CODEOCEAN-F4

lib/runner/strategy.rb

@@ -33,7 +33,7 @@ class Runner::Strategy
     raise NotImplementedError
   end
 
-  def retrieve_files(path:, recursive:, privileged_execution:)
+  def retrieve_files(path: './', recursive: true, privileged_execution: false)
     raise NotImplementedError
   end
 

lib/runner/strategy/docker_container_pool.rb

@@ -104,7 +104,7 @@ class Runner::Strategy::DockerContainerPool < Runner::Strategy
     Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Finished copying files" }
   end
 
-  def retrieve_files(path:, recursive:, privileged_execution:)
+  def retrieve_files(path: './', recursive: true, privileged_execution: false)
     # The DockerContainerPool does not support retrieving files from the runner.
   end
 

lib/runner/strategy/null.rb

@@ -25,7 +25,7 @@ class Runner::Strategy::Null < Runner::Strategy
 
   def copy_files(_files); end
 
-  def retrieve_files(path:, recursive:, privileged_execution: false); end
+  def retrieve_files(path: './', recursive: true, privileged_execution: false); end
 
   def download_file(_file, privileged_execution: false, &_block) # rubocop:disable Lint/UnusedMethodArgument for the keyword argument
     raise Runner::Error.new