Add missing end of sentence in docs (GH-27280) (GH-27419)

(cherry picked from commit 531e2fbc52ce07a9cf37e0db05a5337e404dfccd)

Co-authored-by: Adrian Garcia Badaracco <1755071+adriangb@users.noreply.github.com>
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst
index d57f8ce..897efc2 100644
--- a/Doc/library/concurrent.futures.rst
+++ b/Doc/library/concurrent.futures.rst
@@ -350,7 +350,7 @@
        If the future is cancelled before completing then :exc:`.CancelledError`
        will be raised.
 
-       If the call raised, this method will raise the same exception.
+       If the call raised an exception, this method will raise the same exception.
 
     .. method:: exception(timeout=None)