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

diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index 96989bd..1e90294 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -497,6 +497,7 @@
       There is no return value.
 
    .. method:: locked()
+
       Return true if the lock is acquired.