patch 8.1.1568: strftime() test fails on MS-Windows

Problem:    Strftime() test fails on MS-Windows.
Solution:   Skip the check for using the $TZ environment variable.

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1568,
 /**/
     1567,
 /**/