docs: reflect behavior of diagnostics bufnr nil (#1879)

doc/telescope.txt

@@ -1564,8 +1564,9 @@ builtin.diagnostics({opts})                  *telescope.builtin.diagnostics()*
         {opts} (table)  options to pass to the picker
 
     Options: ~
-        {bufnr}          (string|number)   if nil get diagnostics for all open
-                                           buffers. Use 0 for current buffer
+        {bufnr}          (number|nil)      Buffer number to get diagnostics
+                                           from. Use 0 for current buffer or
+                                           nil for all buffers
         {severity}       (string|number)   filter diagnostics by severity name
                                            (string) or id (number)
         {severity_limit} (string|number)   keep diagnostics equal or more

lua/telescope/builtin/init.lua

@@ -439,7 +439,7 @@ builtin.lsp_dynamic_workspace_symbols = require_on_exported_call("telescope.buil
 --- - Default keymaps:
 ---   - `<C-l>`: show autocompletion menu to prefilter your query with the diagnostic you want to see (i.e. `:warning:`)
 ---@param opts table: options to pass to the picker
----@field bufnr string|number: if nil get diagnostics for all open buffers. Use 0 for current buffer
+---@field bufnr number|nil: Buffer number to get diagnostics from. Use 0 for current buffer or nil for all buffers
 ---@field severity string|number: filter diagnostics by severity name (string) or id (number)
 ---@field severity_limit string|number: keep diagnostics equal or more severe wrt severity name (string) or id (number)
 ---@field severity_bound string|number: keep diagnostics equal or less severe wrt severity name (string) or id (number)