Fix test when Ruby is verbose

	The test added in 90a80eb0 fails if Ruby is verbose, it outputs the
	following line to stderr:

	    RUBY_GC_HEAP_INIT_SLOTS=100 (default value: 10000)
	---
	 test/ruby/test_gc.rb | 2 +-
	 1 file changed, 1 insertion(+), 1 deletion(-)