fix: correcting some problem with review mode

[ElricleNecro]

Trying to fix some problem in the review command of the plugin, as describe in this github discussion.

It concern mainly the following problems:

• Error executing lua: Vim:E5300: Expected a Number or a String
  stack traceback:
    [C]: in function 'bufnr'
    ...lazy/gitlab.nvim/lua/gitlab/actions/discussions/init.lua:456: in function 'jump_to_file'
    ...lazy/gitlab.nvim/lua/gitlab/actions/discussions/init.lua:832: in function <...lazy/gitlab.nvim/lua/gitlab/actions/discussions/init.lua:830>
  

• E5108: Error executing lua: ...lazy/gitlab.nvim/lua/gitlab/actions/discussions/init.lua:467: Cursor position outside buffer
  stack traceback:
  	[C]: in function 'nvim_win_set_cursor'
  	...lazy/gitlab.nvim/lua/gitlab/actions/discussions/init.lua:467: in function 'jump_to_file'
  	...lazy/gitlab.nvim/lua/gitlab/actions/discussions/init.lua:834: in function <...lazy/gitlab.nvim/lua/gitlab/actions/discussions/init.lua:832>
  

[harrisoncramer]

Thank you for noticing this, it was a regression that was introduced after a recent major refactor of the plugin! I don't often use these keybindings and hadn't noticed.