patch 9.0.1961: 'listchars' completion misses "multispace" and "leadmultispace"

Problem:  Cmdline completion for 'listchars' fields doesn't include
          "multispace" and "leadmultispace" (after 9.0.1958).
Solution: Include "multispace" and "leadmultispace" in lcstab.

closes: #13225

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 3d53efd..32d4910 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -517,10 +517,12 @@
   call assert_equal(getcompletion('set printoptions=', 'cmdline')[0], 'top')
   call assert_equal(getcompletion('set wincolor=', 'cmdline')[0], 'SpecialKey')
 
-  call assert_equal(getcompletion('set listchars+=', 'cmdline')[0], 'eol')
-  call assert_equal(getcompletion('setl listchars+=', 'cmdline')[0], 'eol')
-  call assert_equal(getcompletion('set fillchars+=', 'cmdline')[0], 'stl')
-  call assert_equal(getcompletion('setl fillchars+=', 'cmdline')[0], 'stl')
+  call assert_equal('eol', getcompletion('set listchars+=', 'cmdline')[0])
+  call assert_equal(['multispace', 'leadmultispace'], getcompletion('set listchars+=', 'cmdline')[-2:])
+  call assert_equal('eol', getcompletion('setl listchars+=', 'cmdline')[0])
+  call assert_equal(['multispace', 'leadmultispace'], getcompletion('setl listchars+=', 'cmdline')[-2:])
+  call assert_equal('stl', getcompletion('set fillchars+=', 'cmdline')[0])
+  call assert_equal('stl', getcompletion('setl fillchars+=', 'cmdline')[0])
 
   "
   " Unique string options below