Ruby: Add CFG test for forward parameters

ruby/ql/test/library-tests/controlflow/graph/Cfg.expected

@@ -2398,7 +2398,7 @@ cfg.rb:
 #-----|  -> yield ...
 
 #  194| call to run_block
-#-----|  -> exit cfg.rb (normal)
+#-----|  -> forward_param
 
 #  194| self
 #-----|  -> { ... }
@@ -2426,6 +2426,17 @@ cfg.rb:
 #  194| x
 #-----|  -> call to puts
 
+#  196| enter forward_param
+#-----|  -> a
+
+#  196| forward_param
+#-----|  -> exit cfg.rb (normal)
+
+#  196| a
+#-----|  -> b
+
+#  196| b
+
 desugar.rb:
 #    1| enter m1
 #-----|  -> x

ruby/ql/test/library-tests/controlflow/graph/cfg.rb

@@ -193,6 +193,10 @@ end
 
 run_block { |x|puts x }
 
+def forward_param(a, b, ...)
+  bar(b, ...)
+end
+
 __END__
 
 Some ignored nonsense