test: monad stack with multiple ExceptT

cc @Kha :)

tests/lean/run/doNotation5.lean

@@ -0,0 +1,29 @@
+new_frontend
+
+abbrev M := ExceptT String $ ExceptT Nat $ StateM Nat
+
+def inc (x : Nat) : M Unit := do
+if (← get) >= 100 then
+  throwThe Nat ((← get) + x)
+modify (· + x)
+
+def dec (x : Nat) : M Unit := do
+if (← get) - x == 0 then
+  throw "balance is zero"
+modify (· - x)
+
+def f (x y : Nat) : M Nat := do
+try
+  inc x
+  dec y
+  get
+catch ex : String =>
+  dbgTrace! "string exception " ++ toString ex
+  pure 1000
+catch ex : Nat =>
+  dbgTrace! "nat exception " ++ toString ex
+  pure ex
+
+#eval (f 10 20).run 1000
+#eval (f 10 200).run 10
+#eval (f 10 20).run 30