fix(actions): copy hash to unnamed register instead of clipboard (sindrets#606)

Use the unnamed register (") instead of the system clipboard (+) when
copying commit hashes. This is more consistent with Vim conventions and
works regardless of clipboard support.

Fixes sindrets#604

Author: jecaro

lua/diffview/scene/views/file_history/listeners.lua

@@ -208,7 +208,7 @@ return function(view)
       if view.panel:is_focused() then
         local item = view.panel:get_item_at_cursor()
         if item then
-          vim.fn.setreg("+", item.commit.hash)
+          vim.fn.setreg('"', item.commit.hash)
           utils.info(string.format("Copied '%s' to the clipboard.", item.commit.hash))
         end
       end