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'.
diff --git a/src/version.c b/src/version.c
index 413c2c1..811a3d6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    438,
+/**/
     437,
 /**/
     436,