patch 8.2.3338: Vim9: no type check when assigning a list range

Problem:    Vim9: no type check when assigning a list range. (Naohiro Ono)
Solution:   Check the member type. (closes #8750)
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 8f8e34c..2eda9a8 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -189,6 +189,12 @@
       call assert_equal([5, 6], l)
   END
   call CheckLegacyAndVim9Success(lines)
+
+  let lines =<< trim END
+    var l = [7]
+    l[:] = ['text']
+  END
+  call CheckDefAndScriptFailure(lines, 'E1012:', 2)
 endfunc
 
 " Test removing items in list