[3.12] gh-114913: Add newline to subprocess doc (GH-114941) (#114942)

*creationflags* is a separate topic from *startupinfo*.
Start sentence with 'If given', like previous sentence.
(cherry picked from commit 1183f1e)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Author: miss-islington

Doc/library/subprocess.rst

@@ -664,7 +664,8 @@ functions.
 
    If given, *startupinfo* will be a :class:`STARTUPINFO` object, which is
    passed to the underlying ``CreateProcess`` function.
-   *creationflags*, if given, can be one or more of the following flags:
+
+   If given, *creationflags*, can be one or more of the following flags:
 
    * :data:`CREATE_NEW_CONSOLE`
    * :data:`CREATE_NEW_PROCESS_GROUP`