Ensure proper environment when using nsz

I have an alias nsz which runs a nix-shell with zsh.
But the $SHELL is still bash.

I now change the SHELL variable in order to use my expected shell in all
circumstances.
I also ensure neovim will use zsh for commands as some of my auto
commands expect this shell for expansion of **.

home/files/zshrc

@@ -49,6 +49,7 @@ nix_subshell () {
     # check for IN_NIX_SHELL
     if [[ "$IN_NIX_SHELL" ]]; then
         prompt_color="yellow"
+        export SHELL=$(which zsh)
     fi
 }
 add-zsh-hook precmd nix_subshell

home/programs/neovim/configuration/plugin/initialconfiguration.vim

@@ -46,3 +46,7 @@ set scrolloff=1000
 " Custom highlighting
 match Todo /TODO\|NOTE\|todo\|TASK/
 match ERROR /♥/
+
+" As I sometimes open neovim inside a nix-shell where default SHELL is bash instead of zsh.
+" This would break some of my autocommands using ** expansion.
+set shell=zsh