patch 9.0.1935: Vim9: not consistent error messages

Problem:  Vim9: not consistent error messages
Solution: Make error messages more consistent. Use "variable" for
          (object/class) member

closes: #13155

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: RestorerZ <restorer@mail2k.ru>
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 2fc7f34..02a37e8 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2181,7 +2181,7 @@
 	    {
 		if (*member == '_')
 		{
-		    semsg(_(e_cannot_access_private_member_str), m->ocm_name);
+		    semsg(_(e_cannot_access_private_variable_str), m->ocm_name);
 		    status = FAIL;
 		}