Ruby: Add test case: array constant barrier guard

This guard isn't yet recognised as a `StringConstArrayInclusionCall`.

Author: hmac

ruby/ql/test/library-tests/dataflow/barrier-guards/barrier-guards.rb

@@ -31,3 +31,11 @@
 end
 
 foo
+
+FOO = ["foo"]
+
+if FOO.include?(foo)
+    foo
+else
+    foo
+end