Doc: add missing capture_output arg to subprocess.run() signature (GH-8374)

(cherry picked from commit 22d131a7f9e4e64486da1d1cddbfed2379517791)

Co-authored-by: Andriy Maletsky <9919211+and800@users.noreply.github.com>
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 5843986..19f6ff3 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -38,8 +38,8 @@
 
 
 .. function:: run(args, *, stdin=None, input=None, stdout=None, stderr=None,\
-                  shell=False, cwd=None, timeout=None, check=False, \
-                  encoding=None, errors=None, text=None, env=None)
+                  capture_output=False, shell=False, cwd=None, timeout=None, \
+                  check=False, encoding=None, errors=None, text=None, env=None)
 
    Run the command described by *args*.  Wait for command to complete, then
    return a :class:`CompletedProcess` instance.