[docs] Update changelog (#12454)

Some additions to the changelog,
that were not added in the relevant PRs.

doc/extdev/appapi.rst

@@ -137,6 +137,8 @@ The application object also provides runtime information as attributes.
 
    Directory for storing built document.
 
+.. autoattribute:: Sphinx.fresh_env_used
+
 Sphinx core events
 ------------------
 

doc/extdev/envapi.rst

@@ -45,6 +45,8 @@ Build environment API
 
    .. autoattribute:: docname
 
+   .. autoattribute:: parser
+
    **Utility methods**
 
    .. automethod:: doc2path