[3.12] pythongh-129892: Doc: Remove unnecessary role directive in graphlib.py (pythonGH-129896) (python#129905)

pythongh-129892: Doc: Remove unnecessary role directive in graphlib.py (pythonGH-129896)

Change `:exec:ValueError` to `ValueError` in `TopologicalSorter.done()` docstring
(cherry picked from commit c537301)

Co-authored-by: Nikola Savic <[email protected]>

Author: miss-islington

Lib/graphlib.py

@@ -154,7 +154,7 @@ def done(self, *nodes):
         This method unblocks any successor of each node in *nodes* for being returned
         in the future by a call to "get_ready".
 
-        Raises :exec:`ValueError` if any node in *nodes* has already been marked as
+        Raises ValueError if any node in *nodes* has already been marked as
         processed by a previous call to this method, if a node was not added to the
         graph by using "add" or if called without calling "prepare" previously or if
         node has not yet been returned by "get_ready".