Fix definition of term_or_dynamic_optional type (#15498)

Fixes #15497

Author: lukaszsamson

lib/elixir/lib/module/types/descr.ex

@@ -76,7 +76,7 @@ defmodule Module.Types.Descr do
 
   @not_set %{optional: 1}
   @term_or_optional Map.put(@term, :optional, 1)
-  @term_or_dynamic_optional Map.put(@term, :dynamic, %{optional: 1})
+  @term_or_dynamic_optional Map.put(@term, :dynamic, @term_or_optional)
   @not_atom_or_optional Map.delete(@term_or_optional, :atom)
 
   @empty_intersection [0, :bdd_bot]

lib/elixir/test/elixir/module/types/descr_test.exs

@@ -1033,6 +1033,12 @@ defmodule Module.Types.DescrTest do
       refute subtype?(if_set(term()), term())
       assert subtype?(if_set(term()), if_set(term()))
       refute subtype?(if_set(term()), if_set(dynamic(term())))
+
+      # Test that union+dynamic optimizations preserves properties
+      t = opt_union(term(), dynamic(not_set()))
+      assert subtype?(term(), t)
+      assert subtype?(dynamic(), t)
+      assert subtype?(dynamic(integer()), t)
     end
 
     test "list" do