fix(builtin.buffers): better buffer in cwd check (#2847)

Previously, using `string.find`, certain characters were taken as regex
special characters leading to bad matches.
New approach takes bufname truncated to the length of cwd and compares
the two strings.

(cherry picked from commit 8b56e9b)

lua/telescope/builtin/__internal.lua

@@ -868,7 +868,8 @@ internal.buffers = function(opts)
  if cwd:sub(-1) ~= Path.path.sep then
  cwd = cwd .. Path.path.sep
  end
- return vim.api.nvim_buf_get_name(bufnr):find(cwd) == nil
+ local bufname_prefix = vim.api.nvim_buf_get_name(bufnr):sub(1, #cwd)
+ return bufname_prefix ~= cwd
  end
 
  local bufnrs = vim.tbl_filter(function(bufnr)