Fix handling orphan documents in the feedback ext
Before this change, the cut-off step was present but the new string
wasn't assigned back and this resulted in `:orphan:` not only re-
injected at the beginning of the document but also left over after
the admonition.
@@ -111,7 +111,7 @@ def _modify_rst_document_source_on_read(
orphan_mark = ':orphan:'
is_orphan = orphan_mark in source[0]
if is_orphan:
- source[0].replace(orphan_mark, '')
+ source[0] = source[0].replace(orphan_mark, '')
else:
orphan_mark = ''
