Add missing File#path call in tests

Spotted this in the test output:

    TestMonitor#test_new_file_permissions_ignore_group_writable_unreadable = /usr/local/lib/ruby/3.1.0/delegate.rb:87: warning: deprecated Object#=~ is called on File; it always returns nil
    0.01 s = .

test/rubygems/comparator/test_monitor.rb

@@ -111,7 +111,7 @@ def test_new_file_permissions_ignore_group_writable_unreadable
     file = Tempfile.new
     begin
       File.chmod(0660, file)
-      assert_equal '  (!) Unexpected permissions: 100660', Gem::Comparator::Monitor.new_file_permissions(file, true)
+      assert_equal '  (!) Unexpected permissions: 100660', Gem::Comparator::Monitor.new_file_permissions(file.path, true)
     ensure
       file.unlink
     end