Add missing period in distutils.dep_util.newer_group doc (GH-11003)

(cherry picked from commit c9566b8c)
Co-authored-by: Andre Delfino <adelfino@gmail.com>

Doc/distutils/apiref.rst

@@ -934,7 +934,7 @@ timestamp dependency analysis.
 .. function:: newer_group(sources, target[, missing='error'])
 
    Return true if *target* is out-of-date with respect to any file listed in
-   *sources*  In other words, if *target* exists and is newer than every file in
+   *sources*.  In other words, if *target* exists and is newer than every file in
    *sources*, return false; otherwise return true. *missing* controls what we do
    when a source file is missing; the default (``'error'``) is to blow up with an
    :exc:`OSError` from  inside :func:`os.stat`; if it is ``'ignore'``, we silently