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)