defaults: shortmess+=F (#8619)

Because we default to laststatus=2 (statusline is always visible), the
:edit message is not useful.

ref #6289

src/nvim/options.lua

@@ -2123,7 +2123,7 @@ return {
       type='string', list='flags', scope={'global'},
       vim=true,
       varname='p_shm',
-      defaults={if_true={vi="", vim="filnxtToO"}}
+      defaults={if_true={vi="", vim="filnxtToOF"}}
     },
     {
       full_name='showbreak', abbreviation='sbr',