Bump language version for pkg/dtd

Extracted from https://dart-review.googlesource.com/c/sdk/+/397164
Which migrates the sdk to resolve as a pub workspace

Pub workspaces requires a language version of 3.5.

Change-Id: I1b9c107764dda434ccd4a8530b779d1d132fb070
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/412641
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Sigurd Meldgaard <[email protected]>

Author: sigurdm

pkg/dtd/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.4.1-wip
+
+- Update SDK constraints to `^3.5.0`.
+
 ## 2.4.0
 
 - Bump `unified_analytics` dependency to ^7.0.0.

pkg/dtd/pubspec.yaml

@@ -4,7 +4,7 @@ description: A package for communicating with the Dart Tooling Daemon.
 repository: https://github.com/dart-lang/sdk/tree/main/pkg/dtd
 
 environment:
-  sdk: ^3.0.0
+  sdk: ^3.5.0
 
 dependencies:
   json_rpc_2: ^3.0.2