Add expectations after submit in attachments specs

There were cases where we clicked the button to submit the form and
immediately we visited a different page.

In the past, we've had similar code produce PG::ProtocolViolation errors
in similar situations. Since we've had these errors a few times in the
nested imageable specs, there's a chance they're related to the absence
of the expectation.

Although I'm not even remotely sure this will fix these issues, at least
we now follow the convention of making expectations after every request.

Note we're changing both the nested imageable and nested documentable
specs. Only the nested imageable would need to be changed because it's
the one where there's a `visit` inside the
`imageable_redirected_to_resource_show_or_navigate_to` method. I'm
changing both for consistency.

spec/shared/system/nested_documentable.rb

@@ -210,6 +210,8 @@ shared_examples "nested documentable" do |login_as_name, documentable_factory_na
       documentable_attach_new_file(file_fixture("empty.pdf"))
       click_on submit_button
 
+      expect(page).to have_content documentable_success_notice
+
       documentable_redirected_to_resource_show_or_navigate_to
 
       expect(page).to have_content "Documents"
@@ -232,6 +234,9 @@ shared_examples "nested documentable" do |login_as_name, documentable_factory_na
       end
 
       click_on submit_button
+
+      expect(page).to have_content documentable_success_notice
+
       documentable_redirected_to_resource_show_or_navigate_to
 
       expect(page).to have_content "Documents (#{documentable.class.max_documents_allowed})"

spec/shared/system/nested_imageable.rb

@@ -184,6 +184,9 @@ shared_examples "nested imageable" do |imageable_factory_name, path, imageable_p
       expect(page).to have_selector ".loading-bar.complete"
 
       click_on submit_button
+
+      expect(page).to have_content imageable_success_notice
+
       imageable_redirected_to_resource_show_or_navigate_to(imageable)
 
       expect(page).to have_selector "figure img"