Remove trailing slash from releasenote job sphinx_output_src

The extra trailing slash causes the jobs to copy the content of
the folder instead of the `html` itself.  This patch resolves this
by removing the trailing slash to copy the folder itself.

Change-Id: I7cd8286cc73bf463a7e6b704bd191e0572aef642

playbooks/releasenotes/post.yaml

@@ -2,5 +2,5 @@
   roles:
     - role: fetch-tox-output
     - role: fetch-sphinx-output
-      sphinx_output_src: "{{ zuul.project.src_dir }}/releasenotes/build/html/"
+      sphinx_output_src: "{{ zuul.project.src_dir }}/releasenotes/build/html"
       zuul_executor_dest: "{{ zuul.executor.log_root }}"