fix(highlights): previewer show correct highlight group (#3305)

Fixes a minor bug in the builtin highlights picker where having
`Comment` selected in the picker shows `SpecialComment` in the
previewer. Only happens when the selected highlight is a suffix of
another highlight and the other highlight occurs first.

Author: cameronr

lua/telescope/previewers/buffer_previewer.lua

@@ -1116,7 +1116,7 @@ previewers.highlights = defaulter(function(_)
       vim.schedule(function()
         vim.api.nvim_buf_call(self.state.bufnr, function()
           vim.cmd "keepjumps norm! gg"
-          vim.fn.search(entry.value .. " ")
+          vim.fn.search("^" .. entry.value .. " ")
           local lnum = vim.api.nvim_win_get_cursor(self.state.winid)[1]
           -- That one is actually a match but its better to use it like that then matchadd
           pcall(vim.api.nvim_buf_clear_namespace, self.state.bufnr, ns_previewer, 0, -1)