Fix missing success-responses anchor

Closes #59916

GitOrigin-RevId: c76f0db
Change-Id: I6db3edff877ab1807509394c45272f6f8a9c7267
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404802
Commit-Queue: Devon Carew <[email protected]>
Reviewed-by: Devon Carew <[email protected]>

Author: mabdelaal86

pkg/dtd_impl/dtd_protocol.md

@@ -905,7 +905,7 @@ code | message | meaning
 142 | Permission denied | Permission has been denied for the requested action.
 143 | File scheme expected on uri | The uri parameter should be passed as a uri with a file scheme.
 
- Success Responses
+### Success Responses
 
 Methods that respond with `Success` do so with the following RPC.