patch 8.1.2276: MS-Windows: session test leaves files behind

Problem:    MS-Windows: session test leaves files behind.
Solution:   Wipe out buffers before deleting the directory. (closes #5187)
diff --git a/src/version.c b/src/version.c
index 44149ff..fc6808b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2276,
+/**/
     2275,
 /**/
     2274,