Fix Lock.locked() to remove extra bold highlighting (GH-18042) (#18043)

(cherry picked from commit ef8844f1bcbea994a2a69b5a70309369d08b555c)

Co-authored-by: Grant Jenks <grant.jenks@gmail.com>

Co-authored-by: Grant Jenks <grant.jenks@gmail.com>
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index 93ea4bd..f4b58d3 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -489,6 +489,7 @@
       There is no return value.
 
    .. method:: locked()
+
       Return true if the lock is acquired.