Fix issue with testing.nu in 0.101.1 (#1023)

nushell/nushell#14741 has surfaced an issue with
an incorrect signature in `testing.nu` which caused it to fail
completely. This fixes the signature and allows tests to run properly.

Author: NotTheDr01ds

stdlib-candidate/testing.nu

@@ -22,7 +22,7 @@ def valid-annotations [] {
 # Returns a table containing the list of function names together with their annotations (comments above the declaration)
 def get-annotated [
     file: path
-]: path -> table<function_name: string, annotation: string> {
+]: nothing -> table<function_name: string, annotation: string> {
     let raw_file = (
         open $file
         | lines