patch 9.0.0276: 'buftype' values not sufficiently tested

Problem:    'buftype' values not sufficiently tested.
Solution:   Add and extend tests with 'buftype' values. (closes #10988)
diff --git a/src/version.c b/src/version.c
index e32f990..a0a7210 100644
--- a/src/version.c
+++ b/src/version.c
@@ -724,6 +724,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    276,
+/**/
     275,
 /**/
     274,