Rename test option to stop confusing the test system

On python 3.11 the previous code gave a warning:

tests/test_cliUtils.py::MWOptionDecoratorTest::test_option
   .../python3.11/unittest/case.py:678: DeprecationWarning: It is deprecated to return a value
           that is not None from a test case (<lsst.daf.butler.cli.utils.MWOptionDecorator object at 0x2ae76e790>)
   return self.run(*args, **kwds)

tests/test_cliUtils.py

@@ -241,22 +241,22 @@ def cli(things):
 class MWOptionDecoratorTest(unittest.TestCase):
     """Tests for the MWOptionDecorator class."""
 
-    test_option = MWOptionDecorator("-t", "--test", multiple=True)
+    _test_option = MWOptionDecorator("-t", "--test", multiple=True)
 
     def testGetName(self):
         """Test getting the option name from the MWOptionDecorator."""
-        self.assertEqual(self.test_option.name(), "test")
+        self.assertEqual(self._test_option.name(), "test")
 
     def testGetOpts(self):
         """Test getting the option flags from the MWOptionDecorator."""
-        self.assertEqual(self.test_option.opts(), ["-t", "--test"])
+        self.assertEqual(self._test_option.opts(), ["-t", "--test"])
 
     def testUse(self):
         """Test using the MWOptionDecorator with a command."""
         mock = MagicMock()
 
         @click.command()
-        @self.test_option()
+        @self._test_option()
         def cli(test):
             mock(test)
 
@@ -271,7 +271,7 @@ def testOverride(self):
         mock = MagicMock()
 
         @click.command()
-        @self.test_option(multiple=False)
+        @self._test_option(multiple=False)
         def cli(test):
             mock(test)