Increase sub-task timeout for web_tool_tests_1_2 (#169277)

For more details, @flar did a great job explaining it in
https://github.com/flutter/flutter/issues/169168.

This PR is a one-off fix for the `web_tool_tests_1_2` shard that has
been timing out and bringing the tree down with it. The shard was marked
`bringup` [here](https://github.com/flutter/flutter/pull/168871). After
increasing the sub-task timeout, let's watch it and if it becomes
consistently green, we will remove the `bringup` status.

Partial fix for https://github.com/flutter/flutter/issues/168863
(partial because I still want to remove `bringup` before I consider the
issue fixed)

.ci.yaml

@@ -6566,7 +6566,7 @@ targets:
       subshard: "1_2"
       tags: >
         ["framework", "hostonly", "shard", "windows"]
-      test_timeout_secs: "2700"
+      test_timeout_secs: "3600" # 60 minutes to match the global `timeout` property.
     runIf:
       - dev/**
       - packages/flutter_tools/**