Generic/UnnecessaryFinalModifier: improve code coverage

This commit add one more test case file to exercise defensive code that
makes the sniff bail early if the class has no body.

Author: rodrigoprimo

src/Standards/Generic/Tests/CodeAnalysis/UnnecessaryFinalModifierUnitTest.2.inc

@@ -0,0 +1,5 @@
+<?php
+
+// Intentional parse error (class without body). Testing that the sniff is *not* triggered
+// in this case.
+final class Missing_Body