Bug #1753406: missing \versionadded for subprocess.check_call.

(backport from rev. 56364)

Doc/lib/libsubprocess.tex

@@ -144,6 +144,8 @@ The arguments are the same as for the Popen constructor.  Example:
 \begin{verbatim}
     check_call(["ls", "-l"])
 \end{verbatim}
+
+\versionadded{2.5}
 \end{funcdesc}
 
 \subsubsection{Exceptions}