patch 9.0.1880: Vim9: Need more tests for inheritance

Problem:  Vim9: Need more tests for inheritance
Solution: Add access tests and fixes.

`inside_class` fix from yegappan. `object_index_from_itf_index` fix
access of member on class extending class implementing interface.

Based on tests from Vim9: Class/Object member variable access control #12979

closes: #13032
related: #12979

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ernie Rael <errael@raelity.com>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/version.c b/src/version.c
index 4703b42..a3d6ed0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1880,
+/**/
     1879,
 /**/
     1878,