patch 8.1.0023: gcc 8.1 warns for use of strncpy()

Problem:    gcc 8.1 warns for use of strncpy(). (John Marriott)
Solution:   Use mch_memmove() instead of STRNCPY().

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    23,
 /**/
     22,
 /**/