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.

lua/telescope/builtin/__internal.lua

@@ -886,7 +886,8 @@ 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)