[ruby/optparse] Fix the test failure i ruby/ruby

```
$ make test-all TESTS=test/optparse/
...

[148/178] TestOptionParserDidYouMean#test_raise_unknown = 0.00 s
  1) Failure:
TestOptionParserDidYouMean#test_raise_unknown [/home/mame/work/ruby/test/optparse/test_optparse.rb:106]:
<["--bar"]> expected but was
<[]>.
```

In the old test/unit (bundled in ruby/ruby), when a test class inherits from
another test class, the child class runs all the tests defined in the parent
class.
However, it looks like the new test/unit does not do so. This is because the
test failure does not occur in ruby/optparse.

As a tentative solution, this changes the option names in TestOptionParser to
avoid the name conflict with TestOptionParserDidYouMean.

https://github.com/ruby/optparse/commit/fee86ef7a4

test/optparse/test_optparse.rb

@@ -99,14 +99,14 @@ class TestOptionParser < Test::Unit::TestCase
   end
 
   def test_raise_unknown
-    @opt.def_option('--foo [ARG]') {|arg| @foo = arg}
+    @opt.def_option('--my-foo [ARG]') {|arg| @foo = arg}
     assert @opt.raise_unknown
 
     @opt.raise_unknown = false
-    assert_equal(%w[--bar], @opt.parse(%w[--foo --bar]))
+    assert_equal(%w[--my-bar], @opt.parse(%w[--my-foo --my-bar]))
     assert_nil(@foo)
 
-    assert_equal(%w[--bar], @opt.parse(%w[--foo x --bar]))
+    assert_equal(%w[--my-bar], @opt.parse(%w[--my-foo x --my-bar]))
     assert_equal("x", @foo)
   end