patch 9.1.0831: 'findexpr' can't be used as lambad or Funcref

Problem:  'findexpr' can't be used for lambads
          (Justin Keyes)
Solution: Replace the findexpr option with the findfunc option
          (Yegappan Lakshmanan)

related: #15905
closes: #15976

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 35b7d48..bd9da73 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -1570,7 +1570,7 @@
 
 " Test for changing options in a sandbox
 func Test_opt_sandbox()
-  for opt in ['backupdir', 'cdpath', 'exrc', 'findexpr']
+  for opt in ['backupdir', 'cdpath', 'exrc', 'findfunc']
     call assert_fails('sandbox set ' .. opt .. '?', 'E48:')
     call assert_fails('sandbox let &' .. opt .. ' = 1', 'E48:')
   endfor