patch 9.1.1409: using f-flag in 'complete' conflicts with Neovim

Problem:  using f-flag in 'complete' conflicts with Neovims filename
          completion (glepnir, after v9.1.1301).
Solution: use upper-case "F" flag for completion functions
          (Girish Palya).

fixes: #17347
closes: #17378

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 1f71e1f..8679198 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -274,7 +274,7 @@
   call assert_fails('set complete=ix', 'E535:')
   call assert_fails('set complete=x', 'E539:')
   call assert_fails('set complete=..', 'E535:')
-  set complete=.,w,b,u,k,\ s,i,d,],t,U,f,o
+  set complete=.,w,b,u,k,\ s,i,d,],t,U,F,o
   call assert_fails('set complete=i^-10', 'E535:')
   call assert_fails('set complete=i^x', 'E535:')
   call assert_fails('set complete=k^2,t^-1,s^', 'E535:')
@@ -282,13 +282,13 @@
   call assert_fails('set complete=kfoo^foo2', 'E535:')
   call assert_fails('set complete=kfoo^', 'E535:')
   call assert_fails('set complete=.^', 'E535:')
-  set complete=.,w,b,u,k,s,i,d,],t,U,f,o
+  set complete=.,w,b,u,k,s,i,d,],t,U,F,o
   set complete=.
   set complete=.^10,t^0
-  set complete+=ffuncref('foo'\\,\ [10])
-  set complete=ffuncref('foo'\\,\ [10])^10
+  set complete+=Ffuncref('foo'\\,\ [10])
+  set complete=Ffuncref('foo'\\,\ [10])^10
   set complete&
-  set complete+=ffunction('g:foo'\\,\ [10\\,\ 20])
+  set complete+=Ffunction('g:foo'\\,\ [10\\,\ 20])
   set complete&
 endfun