patch 8.2.2693: Vim9: locked script variable can be changed

Problem:    Vim9: locked script variable can be changed.
Solution:   Check legacy script variable for being locked. (issue #8031)
diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index c062052..867afaf 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -1355,7 +1355,17 @@
     enddef
     SetLocked()
   END
-  CheckScriptFailure(lines, 'E741: Value is locked: name')
+  CheckScriptFailure(lines, 'E741: Value is locked: name', 1)
+
+  lines =<< trim END
+    let s:legacy = 'one'
+    lockvar s:legacy
+    def SetLocked()
+      s:legacy = 'two'
+    enddef
+    call SetLocked()
+  END
+  CheckScriptFailure(lines, 'E741: Value is locked: s:legacy', 1)
 
   lines =<< trim END
     vim9script
@@ -1365,7 +1375,7 @@
     SetGlobalConst()
     g:globConst = 234
   END
-  CheckScriptFailure(lines, 'E741: Value is locked: globConst')
+  CheckScriptFailure(lines, 'E741: Value is locked: globConst', 1)
   unlet g:globConst
 
   lines =<< trim END