Fix formatting error in rst plugin template (#38956)

The hyperlink syntax used is wrong and the resulting
rendered documents have broken links.

docs/templates/plugin.rst.j2

@@ -407,5 +407,5 @@ Author
 {%   if plugin_type == 'module' %}
     If you notice any issues in this documentation you can `edit this document <https://github.com/ansible/ansible/edit/devel/lib/ansible/modules/@{ source }@?description=%3C!---%20Your%20description%20here%20--%3E%0A%0A%2Blabel:%20docsite_pr>`_ to improve it.
 {% else %}
-    If you notice any issues in this documentation you can `edit this document <https://github.com/ansible/ansible/edit/devel/lib/ansible/plugins/@{ plugin_type }@/@{ source }@_` to improve it.
+    If you notice any issues in this documentation you can `edit this document <https://github.com/ansible/ansible/edit/devel/lib/ansible/plugins/@{ plugin_type }@/@{ source }@`_ to improve it.
 {% endif %}