patch 8.2.0383: wrong feature check causes test not to be run

Problem:    Wrong feature check causes test not to be run.
Solution:   Use CheckFunction instead of CheckFeature. (Ozaki Kiichi,
            closes #5781)
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index af767d2..2034aec 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -1775,7 +1775,7 @@
 
 func Test_job_start_in_timer()
   CheckFeature timers
-  CheckFeature reltimefloat
+  CheckFunction reltimefloat
 
   func OutCb(chan, msg)
     let g:val += 1