Add dimensions to release builds. (#126117)

Release builds running in dart internal require the dimensions to be set explicitly at the target level in ci.yaml.

Bug: https://github.com/flutter/flutter/issues/126116

.ci.yaml

@@ -330,6 +330,8 @@ targets:
     recipe: flutter/flutter
     presubmit: false
     timeout: 90 # https://github.com/flutter/flutter/issues/120901
+    dimensions:
+      os: "Linux"
     properties:
       cores: "32"
       dependencies: >-
@@ -4840,6 +4842,8 @@ targets:
       task_name: flutter_packaging
       tags: >
         ["framework", "hostonly", "shard", "linux"]
+    dimensions:
+      os: "Linux"
 
   - name: Mac flutter_packaging
     recipe: packaging/packaging
@@ -4855,6 +4859,7 @@ targets:
         ["framework", "hostonly", "shard", "mac"]
     dimensions:
       cpu: "x86"
+      os: "Mac"
 
 
   - name: Mac_arm64 flutter_packaging
@@ -4871,6 +4876,7 @@ targets:
         ["framework", "hostonly", "shard", "mac"]
     dimensions:
       cpu: "arm64"
+      os: "Mac"
 
   - name: Windows flutter_packaging
     recipe: packaging/packaging
@@ -4884,6 +4890,8 @@ targets:
       task_name: flutter_packaging
       tags: >
         ["framework", "hostonly", "shard", "windows"]
+    dimensions:
+      os: "Windows"
 
 
   - name: Linux docs_deploy_beta
@@ -4906,6 +4914,8 @@ targets:
       validation: docs_deploy
       validation_name: Docs_deploy
       firebase_project: master-docs-flutter-dev
+    dimensions:
+      os: "Linux"
 
   - name: Linux docs_deploy_stable
     recipe: flutter/flutter
@@ -4927,3 +4937,5 @@ targets:
       validation: docs_deploy
       validation_name: Docs_deploy
       firebase_project: docs-flutter-dev
+    dimensions:
+      os: "Linux"