patch 8.1.2256: test for ":term ++shell" fails on MS-Windows

Problem:    Test for ":term ++shell" fails on MS-Windows.
Solution:   Accept failure of "dir" executable.
diff --git a/src/version.c b/src/version.c
index 4315a17..182352d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2256,
+/**/
     2255,
 /**/
     2254,