patch 8.1.2098: mksession test fails on MS-Windows

Problem:    mksession test fails on MS-Windows.
Solution:   Skip testing with backslashes on MS-Windows.
diff --git a/src/version.c b/src/version.c
index 736a632..20a0285 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2098,
+/**/
     2097,
 /**/
     2096,