[infra] Update checked in SDKs to 2.4.0

Change-Id: I4c315a0c61a4c5bf8144aaf4d85ab5ae95dec315
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/108400
Auto-Submit: Alexander Thomas <[email protected]>
Commit-Queue: Jonas Termansen <[email protected]>
Reviewed-by: Jonas Termansen <[email protected]>

Author: athomas

DEPS

@@ -157,7 +157,7 @@ deps = {
   Var("dart_root") + "/tools/sdks": {
       "packages": [{
           "package": "dart/dart-sdk/${{platform}}",
-          "version": "version:2.3.3-dev.0.0",
+          "version": "version:2.4.0",
       }],
       "dep_type": "cipd",
   },