refactor(homebrew): switch to neovim-nightly

Via this tap:

- https://github.com/benjiwolff/homebrew-neovim-nightly

Because you can no longer use `brew install neovim --HEAD` to get a
working install:

- neovim/neovim#28125

You'll get a copy of Neovim _without_ the bundled treesitter parsers,
causing any attempt to edit a Lua (etc) file to yield an ugly error:

    no parser for 'lua' language, see :help treesitter-parser

Once v0.10 is out, I'll be able to switch back to a standard `brew
install neovim` (right now need a pre-release version in order to get
commenting/uncommenting functionality, seeing as I removed
tcomment_vim).

aspects/homebrew/templates/Brewfile.erb

@@ -8,6 +8,7 @@ tap "homebrew/bundle"
 tap "homebrew/services"
 tap "oven-sh/bun"
 tap "tavianator/tap"
+tap "benjiwolff/neovim-nightly"
 
 # General packages.
 brew "ack"
@@ -115,7 +116,7 @@ brew "mosh"
 brew "mpfr"
 brew "msgpack"
 brew "mtr"
-brew "neovim", args: ["HEAD"]
+brew "neovim-nightly"
 brew "nettle"
 brew "nginx"
 brew "ninja"