bpo-41959: Fix grammar around class asyncio.MultiLoopChildWatcher text (GH-22580) (#22865)

While translating the following document to Spanish we found there is a grammar issue on the original documentation.
(cherry picked from commit caff2934f46510920a6169e192707d59e9c55f6b)

Co-authored-by: Raúl Cumplido <raulcumplido@gmail.com>

Co-authored-by: Raúl Cumplido <raulcumplido@gmail.com>
diff --git a/Doc/library/asyncio-policy.rst b/Doc/library/asyncio-policy.rst
index d9d3232..88e69ce 100644
--- a/Doc/library/asyncio-policy.rst
+++ b/Doc/library/asyncio-policy.rst
@@ -219,7 +219,7 @@
 
    This implementation registers a :py:data:`SIGCHLD` signal handler on
    instantiation. That can break third-party code that installs a custom handler for
-   `SIGCHLD`.  signal).
+   :py:data:`SIGCHLD` signal.
 
    The watcher avoids disrupting other code spawning processes
    by polling every process explicitly on a :py:data:`SIGCHLD` signal.