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/eval.c b/src/eval.c
index 3f8ce5f..eaca2f5 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1560,7 +1560,7 @@
 			switch (om->ocm_access)
 			{
 			    case VIM_ACCESS_PRIVATE:
-				semsg(_(e_cannot_access_private_member_str),
+				semsg(_(e_cannot_access_private_variable_str),
 					om->ocm_name);
 				return NULL;
 			    case VIM_ACCESS_READ:
@@ -1569,7 +1569,7 @@
 				    break;
 				if ((flags & GLV_READ_ONLY) == 0)
 				{
-				    semsg(_(e_member_is_not_writable_str),
+				    semsg(_(e_variable_is_not_writable_str),
 					    om->ocm_name, cl->class_name);
 				    return NULL;
 				}