patch 8.2.2753: Vim9: cannot ignore an item in assignment unpack

Problem:    Vim9: cannot ignore an item in assignment unpack.
Solution:   Allow using an underscore.
diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index c35084d..958b7b9 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -256,6 +256,14 @@
     [v1, v2] = [1, 2]
     assert_equal(1, v1)
     assert_equal(2, v2)
+
+    [v1, _, v2, _] = [1, 99, 2, 77]
+    assert_equal(1, v1)
+    assert_equal(2, v2)
+
+    [v1, v2; _] = [1, 2, 3, 4, 5]
+    assert_equal(1, v1)
+    assert_equal(2, v2)
   END
   CheckDefAndScriptSuccess(lines)