Allow assigning both targets and local targets

Particularly useful in tests, because writing `targets` is shorter than
writing `global_targets` and `local_targets`.

spec/models/sdg/relatable_spec.rb

@@ -69,6 +69,18 @@ describe SDG::Relatable do
     end
   end
 
+  describe "#sdg_targets=" do
+    it "assigns both targets and local targets" do
+      global_targets = [SDG::Target[2.2], SDG::Target[1.2]]
+      local_targets = %w[2.2.1 3.1.1].map { |code| create(:sdg_local_target, code: code) }
+
+      relatable.sdg_targets = global_targets + local_targets
+
+      expect(relatable.sdg_global_targets).to match_array global_targets
+      expect(relatable.sdg_local_targets).to match_array local_targets
+    end
+  end
+
   describe "#sdg_local_targets" do
     it "can assign local targets to a model" do
       relatable.sdg_local_targets = [local_target, another_local_target]