fix foreach bug in ruby cfg

Author: aschackmull

ruby/ql/lib/codeql/ruby/controlflow/ControlFlowGraph2.qll

@@ -251,6 +251,8 @@ private module Ast implements AstSig<Location> {
 
   // `ForExpr` would be a match for `ForeachStmt`, but it is desugared.
   class ForeachStmt extends LoopStmt {
+    ForeachStmt() { none() }
+
     Expr getVariable() { none() }
 
     Expr getCollection() { none() }