Update dartdoc to 0.24.1.

Change-Id: I1b088b046dd893aa59753a5eb2ebe1947d0bbc8c
Reviewed-on: https://dart-review.googlesource.com/c/80682
Reviewed-by: Devon Carew <devoncarew@google.com>
Commit-Queue: Janice Collins <jcollins@google.com>

DEPS

@@ -79,7 +79,7 @@ vars = {
   # For more details, see https://github.com/dart-lang/sdk/issues/30164
   "dart_style_tag": "1.2.0",  # Please see the note above before updating.
 
-  "dartdoc_tag" : "v0.24.0",
+  "dartdoc_tag" : "v0.24.1",
   "file_rev": "515ed1dd48740ab14b625de1be464cb2bca4fefd",  # 5.0.6
   "fixnum_tag": "0.10.8",
   "func_rev": "25eec48146a58967d75330075ab376b3838b18a8",