patch 8.2.1857: Vim9: using job_status() on an unused var gives an error

Problem:    Vim9: using job_status() on an unused var gives an error.
Solution:   Return "fail". (closes #7158)
diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 478a1e5..5f5a459 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -74,7 +74,11 @@
 
   if has('channel')
     var chan1: channel
+    assert_equal('fail', ch_status(chan1))
+
     var job1: job
+    assert_equal('fail', job_status(job1))
+
     # calling job_start() is in test_vim9_fails.vim, it causes leak reports
   endif
   if has('float')