Make BeginBlock CFG post-order

ql/src/codeql_ruby/controlflow/internal/ControlFlowGraphImpl.qll

@@ -1108,7 +1108,8 @@ module Trees {
   private class SimplePostOrderStmtSequenceTree extends StmtSequenceTree, PostOrderTree {
     SimplePostOrderStmtSequenceTree() {
       this instanceof StringInterpolationComponent or
-      this instanceof ParenthesizedExpr
+      this instanceof ParenthesizedExpr or
+      this instanceof BeginBlock
     }
 
     final override predicate first(AstNode first) { first(this.getStmt(0), first) }
@@ -1136,7 +1137,8 @@ module Trees {
       not this instanceof EndBlock and
       not this instanceof StringInterpolationComponent and
       not this instanceof Block and
-      not this instanceof ParenthesizedExpr
+      not this instanceof ParenthesizedExpr and
+      not this instanceof BeginBlock
     }
 
     final override predicate propagatesAbnormal(AstNode child) { child = this.getAStmt() }

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

@@ -491,7 +491,7 @@ case.rb:
 
 cfg.rb:
 #    1| enter cfg.rb
-#-----|  -> BEGIN { ... }
+#-----|  -> self
 
 #    1| bar
 #-----|  -> alias ...
@@ -559,10 +559,10 @@ cfg.rb:
 #-----|  -> call to puts
 
 #   15| BEGIN { ... }
-#-----|  -> self
+#-----|  -> bar
 
 #   16| call to puts
-#-----|  -> bar
+#-----|  -> BEGIN { ... }
 
 #   16| self
 #-----|  -> "hello"