patch 8.2.1390: Vim9: type error after storing an option value

Problem:    Vim9: type error after storing an option value.
Solution:   Drop the type after a STOREOPT instruction. (closes #6632)
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 2faa737..c4a6f9a 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -422,6 +422,11 @@
   assert_equal('one', v1)
   assert_equal('two', v2)
   assert_equal(['three'], vrem)
+
+  [&ts, &sw] = [3, 4]
+  assert_equal(3, &ts)
+  assert_equal(4, &sw)
+  set ts=8 sw=4
 enddef
 
 def Test_assignment_vim9script()