Add timeout to local_engine. (flutter/engine#56271)

See https://ci.chromium.org/ui/p/flutter/builders/luci.flutter.prod/Linux%20local_engine_builds.

engine/src/flutter/.ci.yaml

@@ -52,6 +52,8 @@ targets:
     recipe: engine_v2/engine_v2
     properties:
       config_name: local_engine
+    # local_engine schedules a bunch of other builds, so it's likely to timeout waiting for those builds to run.
+    timeout: 180
 
   - name: Linux linux_android_emulator_tests
     bringup: true