Only apply `pwsh` setting on Windows

.config/nvim/lua/config/options.lua

···
 
 opt.relativenumber = false
 opt.wrap = true
-opt.shell = "pwsh"
+if vim.loop.os_uname().sysname == "Windows" then
+  opt.shell = "pwsh"
+end
 
 local function append_val(enum, val)
   enum.append(enum, val)