Fix the changelog links to porting guide to be anonymous

Prevents duplicate reference errors.

packaging/release/Makefile

@@ -26,7 +26,7 @@ summary:
 	@printf '%s\n%s\n%s\n' \
 	'release_summary: |' \
 	'   | Release Date: $(shell date '+%Y-%m-%d')' \
-	'   | `Porting Guide <https://docs.ansible.com/ansible/devel/porting_guides.html>`_' > \
+	'   | `Porting Guide <https://docs.ansible.com/ansible/devel/porting_guides.html>`__' > \
 	../../changelogs/fragments/v${version}_summary.yaml
 
 .PHONY: changelog