Ruby: Add test for protected method visibility

Author: hmac

ruby/ql/test/library-tests/modules/callgraph.expected

@@ -394,3 +394,4 @@ publicMethod
 | private.rb:20:3:21:5 | public2 |
 | private.rb:46:3:47:5 | public |
 | private.rb:71:3:73:5 | call_m1 |
+protectedMethods

ruby/ql/test/library-tests/modules/callgraph.ql

@@ -7,3 +7,5 @@ query predicate unresolvedCall(Call call) { not exists(call.getATarget()) }
 query predicate privateMethod(MethodBase m) { m.isPrivate() }
 
 query predicate publicMethod(MethodBase m) { m.isPublic() }
+
+query predicate protectedMethods(MethodBase m) { m.isProtected() }