Test to ensure content_tag works when fixing #17661

After c2fe0938, which was reverted yesterday, there will likely be
future PRs to address #17661.

The test `actionview/test/template/capture_helper_test.rb
#test_capture_returns_nil_if_the_returned_value_is_not_a_string` should
have errored with c2fe0938, but it was rewritten in the PR to not raise.
My guess is that it may have seemed irrelevant to the content_tag tests
or already covered by them.

This test provides additional protection by being in the content_tag
test suite to explicitly raise a red flag in future cases. It foregoes
some redundancy for safety — at least until #17661 is closed.

actionview/test/template/tag_helper_test.rb

@@ -50,6 +50,11 @@ def test_content_tag_with_block_in_erb
     assert_dom_equal "<div>Hello world!</div>", buffer
   end
 
+  def test_content_tag_with_block_in_erb_containing_non_displayed_erb
+    buffer = render_erb("<%= content_tag(:p) do %><% 1 %><% end %>")
+    assert_dom_equal "<p></p>", buffer
+  end
+
   def test_content_tag_with_block_and_options_in_erb
     buffer = render_erb("<%= content_tag(:div, :class => 'green') do %>Hello world!<% end %>")
     assert_dom_equal %(<div class="green">Hello world!</div>), buffer