Fix RuntimeError when using multiple hash splat operators

When multiple hash splat operators expand hashes of the same type,
duplicate edges were being added to the same vertex, causing `Set#<<`
to raise an error. This can be avoided by using `Vertex#new_vertex`.

Co-Authored-By: Takumi Shotoku <sinsoku.listy@gmail.com>

Author: mame

lib/typeprof/core/ast/value.rb

@@ -307,7 +307,7 @@ def install0(genv)
               h = val.install(genv)
             end
             # TODO: do we want to call to_hash on h?
-            @changes.add_hash_splat_box(genv, h, unified_key, unified_val)
+            @changes.add_hash_splat_box(genv, h, unified_key.new_vertex(genv, self), unified_val.new_vertex(genv, self))
           end
         end
         if @splat

scenario/regressions/hash-with-splat-operator.rb

@@ -0,0 +1,11 @@
+## update
+def opts(prefix)
+  { "#{prefix}_key" => 1 }
+end
+
+def test
+  {
+    **opts(:cat),
+    **opts(:dog)
+  }
+end