Reverts "Remove bringup:true from Linux tool_tests_widget_preview_scaffold (flutter#166687)" (flutter#166700)

<!-- start_original_pr_link -->
Reverts: flutter#166687
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: matanlurey
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: Broke postsubmit ("... not up to date")


https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8718230395584699185/+/u/run_test.dart_for_tool_tests_shard_and_subshard_widget_preview_scaffold/stdout
<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: bkonyi
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {matanlurey}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
New shard seems to be stable and passing consistently.
<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <flutter-engprod-team@google.com>

Author: auto-submit[bot]

.ci.yaml

@@ -1592,6 +1592,7 @@ targets:
   - name: Linux tool_tests_widget_preview_scaffold
     recipe: flutter/flutter_drone
     timeout: 60
+    bringup: true
     properties:
       add_recipes_cq: "true"
       dependencies: >-