patch 8.0.0438: the fnamemodify test may cause later tests to fail

Problem:    The fnamemodify test changes 'shell' in a way later tests may not
            be able to use system().
Solution:   Save and restore 'shell'.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    438,
 /**/
     437,
 /**/