Extend timeout of TestRequire#test_require_with_public_method_missing

Launchable reported that this was the most "flaky" test. Perhaps the
default timeout (10 seconds) is too tight for a test that uses
`GC.stress = true`. I try to relax the limit.

test/ruby/test_require.rb

@@ -979,7 +979,7 @@ class TestRequire < Test::Unit::TestCase
 
   def test_require_with_public_method_missing
     # [Bug #19793]
-    assert_separately(["-W0", "-rtempfile"], __FILE__, __LINE__, <<~RUBY)
+    assert_separately(["-W0", "-rtempfile"], __FILE__, __LINE__, <<~RUBY, timeout: 60)
       GC.stress = true
 
       class Object