Update dartdoc to 4.1.0

Release notes:  https://github.com/dart-lang/dartdoc/releases/tag/v4.1.0

Change-Id: Id0207d7123680be61c388a7d3d2c53357b994c44
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/218065
Auto-Submit: Janice Collins <jcollins@google.com>
Commit-Queue: Janice Collins <jcollins@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>
diff --git a/DEPS b/DEPS
index 726c533..a04e778 100644
--- a/DEPS
+++ b/DEPS
@@ -106,7 +106,7 @@
   # For more details, see https://github.com/dart-lang/sdk/issues/30164
   "dart_style_rev": "08b0294d0a500d5c02168ef57dcb8868d0c3cb48",
 
-  "dartdoc_rev" : "c2f284f09bcc49025fe26e86b2d45e1b546f81a3",
+  "dartdoc_rev" : "520e64977de7a87b2fd5be56e5c2e1a58d55bdad",
   "devtools_rev" : "8881a7caa9067471008a8e00750b161f53cdb843",
   "jsshell_tag": "version:88.0",
   "ffi_rev": "4dd32429880a57b64edaf54c9d5af8a9fa9a4ffb",