fix: error due to concatenating table to string (#2108)

This commit fixes a bug that lead to an error because we tried to
concatenate a table (`err`) to a string. Now we concatenate
`err.message` (a string) to the string.

(cherry picked from commit 2e05e63cdf)

lua/telescope/builtin/__lsp.lua

@@ -58,7 +58,7 @@ end
 local function call_hierarchy(opts, method, title, direction, item)
   vim.lsp.buf_request(opts.bufnr, method, { item = item }, function(err, result)
     if err then
-      vim.api.nvim_err_writeln("Error handling " .. title .. ": " .. err)
+      vim.api.nvim_err_writeln("Error handling " .. title .. ": " .. err.message)
       return
     end