patch 8.2.2060: check for features implemented with "if"

Problem:    Check for features implemented with "if".
Solution:   Use the Check commands. (Ken Takata, closes #7383)
diff --git a/src/testdir/test_fold.vim b/src/testdir/test_fold.vim
index 1377983..505ad02 100644
--- a/src/testdir/test_fold.vim
+++ b/src/testdir/test_fold.vim
@@ -95,9 +95,7 @@
 endfunc
 
 func Test_manual_fold_with_filter()
-  if !executable('cat')
-    return
-  endif
+  CheckExecutable cat
   for type in ['manual', 'marker']
     exe 'set foldmethod=' . type
     new