fix(clipboard): tmux clipboard data may be stale #36787

Problem:
When Nvim wants to paste from tmux, it doesn't tell tmux to read the OS
clipboard first, so it may have stale clipboard state.

Solution:
Tickle `tmux refresh-client -l`, before requesting paste, as recommended
in the tmux manpage. https://man7.org/linux/man-pages/man1/tmux.1.html

Fixes https://github.com/neovim/neovim/issues/36786

Signed-off-by: Elias Assaf <elyas51000@gmail.com>

runtime/autoload/provider/clipboard.vim

@@ -168,7 +168,7 @@ function! s:set_tmux() abort
   else
     let s:copy['+'] = ['tmux', 'load-buffer', '-']
   endif
-  let s:paste['+'] = ['tmux', 'save-buffer', '-']
+  let s:paste['+'] = ['sh', '-c', 'tmux refresh-client -l && sleep 0.05 && tmux save-buffer -']
   let s:copy['*'] = s:copy['+']
   let s:paste['*'] = s:paste['+']
   return 'tmux'