nvim: plugins: Make packer not fetch/pull tags

Upstream repos overwrite tags like release and then PackerSync complains
about failing to update since existing tags would be clobbered after an
update.

nvim/.config/nvim/lua/plugins.lua

@@ -91,4 +91,13 @@ local init = function ()
   use 'christoomey/vim-tmux-navigator'
 end
 
-return require('packer').startup(init)
+local config = {
+  git = {
+    subcommands = {
+      update = 'pull --ff-only --progress --rebase=false --no-tags',
+      fetch  = 'fetch --depth 999999 --progress --no-tags',
+    }
+  }
+}
+
+return require('packer').startup(init, config)