(PUP-1381) make file_setting spec test more robust

A new call to self.resource_type in Puppet::Resource#initialize can cause
the loading of type code as a side effect. This interfered with the mocking
for the test

Puppet::Settings::FileSetting when being converted to a resource
should manage existent files even if 'create_files' is not enabled

Add a stubs call to one of the uncritical expectations so that
additional calls are not considered as spurious.